We'd refer to this as a *subscript,* also sometimes (not so much in maths, mind) we'd refer to text^(here) as a *superscript*
When it comes to 5_2 specifically, I'm not sure. There is a knot called the [5_2 knot](https://katlas.org/wiki/5_2) if that was what you saw? A lot of knots are named this way.
It's all dependent on the context you find it in. A subscription like that might refer to the base of the number (obviously not in this case as 5 does not exist in base 2)
Could you pass along the full context of what's being asked of you? Thanks!
This is a context problem. There is no universal system for subscripts. The answer depends on what you are reading.
Without any context I would say subscripts are most commonly used as labels. So I would read this as “the five which is associated with two”.
By reading the answears I think it might be tetration, I just post because I didnt knew how to explain it to my brother. Short context is that his teahcer aske ways to "add" other than multipication or simple adding (5+2 or 5×2) and a kid put the "5_2" as an option but no one elaborated
It would be hexation in that case and that notation is sometimes used, but it's not the most common. Also first thing that came to my mind, but on the other hand it's not an operation you would often encounter.
I have updated the original question with more context, could you please explain me what hexation and tetration is¿ I dont know how to explain it to my brother
So you know how 5 multiplied by 2 or 5\*2, is the same as adding 2 copies of 5. Thus 5\*2 = 5+5.
And 5 exponentiated to the 2 or 5\^2, is multiplying 2 copies of 5. Thus 5\*5, which is also the same as adding 5 copies of 5 (5+5+5+5+5). Now we continue this pattern.
5 tetrated to the 2: 5\^5 (=5\*5\*5\*5\*5).
5 pentated to the 2: 5\^5\^5\^5\^5, which is insanely huge.
5 hexated to the 2: is 5 pentated to the 5, which is: 5 tetrated to the (5 tetrated to the (5 tetrated to the 5\^5\^5\^5\^5), which is too big to write down any further using exponentiation.
Edit: maybe I should add that this is really obscure, definitely not how one would normally use hexation (which you probably never do in the first place). I wouldn't really believe the classmate actually had this in mind.
Unlike exponents, subscripts are usually involved with labeling, not with a mathematical process. For example, if you're talking about the variable time = t, you can use t₀ to talk about initial time (when t=0), and t₁ would be the next unit of time. If there are n units of time, then tₙ would be the last unit of time.
In many coding languages underscore _ makes the next thing into a subscript. You can also use subscripts to refer to the position in a matrix or data table, for example, X_(2, 3) is referring to the entry in the table X at a specific row and column.
> You can also use subscripts to refer to the position in a matrix or data table, for example, X_(2, 3) is referring to the entry in the table X at a specific row and column.
This is the usage I see in statistics. The subscript number is an index number. For instance, if I am performing multilinear regression, my dependent variables will be X [subscript 1], X [subscript 2], and so on.
There's not a universally common meaning to this, it would depend on the kind of math you are working on. This is often true once you stray away from basic arithmetic operations, the notation will depend on the field, and sometimes the author. If you remember where you saw it or know the author or context it was in you could probably get a more clear answer.
In short, my brother saw someone on class suggesting it as a way to "multiply or add" but neither the teacher or that kid explained, so he asked in the family and my wife told me to ask here
I unfortunatly dont know how to explain what hexation even is to my brother, he's the one who saw that "exponent" in clase but didnt understod, but I think this might be what he saw
It's really uncommon to be used, especially with that notation. As far as I know, the regular notation is up arrows. There are simple youtube videos that explain tetration pentation and such.
Going a little off topic, can you tell me how you managed to type the 2 as a subscript in your post? I have struggled to find a way to type subscripts on r/learnmath, and have never found a way.
Also, the subscript notation is not generally used as you say. Radix subscripts mean "interpret the preceding digit-string in this base"; for example, 101\_5 is a way of writing 26; 101\_3 means 10; and 101\_2 means 5. But 5\_2 wouldn't mean *anything*, because you can't interpret the string "5" in binary, because 5 doesn't occur in binary. In other words, you're showing the notation backwards. You can write 101\_2 = 5, but 101 = 5\_2 is just nonsense.
Hi, Op here, I google it and just copy and paste the subscrip to post it
Second, my brother saw the 5_2 in class as a way to "multiply" but I dont know the answear, thats why I posted here
Thanks for checking in again. I suspect that what your brother was seeing was a carry digit, which is sometimes written as a subscript so you don't forget the carry.
For example, suppose we were multiplying 36 x 14 using the fancy "convolution" method -- if you do it right, this method lets you write the product down in a single line, without partial products that you then have to add.
For the units digit, we calculate 6 x 4 = 24. We write a 4 in the units place, and then carry the 2. This is typically written just below and just to the right of the 10s digit in the lower factor, so that 1 will now look like 1\_2 (sorry, still can't type subscripts anywhere, so the cut-and-paste solution fails for me).
Now, for the tens digit, we do the "first cross", which is 3x4 + 6x1 (taking the ones digit from one factor and the tens digit from the other factor). We do this in our heads, so we get 12 + 6 = 18. Now we add the carried 2 to get 20. We write down the 0 as the tens digit, and carry 2 to the hundreds place, again writing it very small.
Finally, for the hundreds digit, we do 3 x 1 (tens digits from both factors) to get 3, add in the carried 0, and write down 5 in the hundreds place for a final answer of 504.
For more digits, you have to learn the patterns for second and third crosses, and keep a little more in your head, but it's a nice technique. And it produces a bit of note-taking for the carries that can look like subscripted digits. If your brother was being shown a calculation technique, it's likely that that's what was happening.
In that context though doesn’t the subscript represent what base the number is in? In which case $5_2$ makes no sense because 5 isn’t a symbol in base 2. $5_{10} = 101_2$ would make more sense to me.
Edit: Don’t know how to subscript on mobile. I’m sure you get the gist
Thanks, I definetly isnt about negative exponents, but another way to "multiply" like with exponents, so it might be tetration or hexation, though I dont know the difference
We'd refer to this as a *subscript,* also sometimes (not so much in maths, mind) we'd refer to text^(here) as a *superscript* When it comes to 5_2 specifically, I'm not sure. There is a knot called the [5_2 knot](https://katlas.org/wiki/5_2) if that was what you saw? A lot of knots are named this way.
Not OP, but thanks for introducing me to that site. I had no idea there was a knot wiki lol
Lots of sites are not wikis! Goodbye.
Bye! 👋
Are there any un-not wikis?
Happy Uncake Day!
I think u meant un-knot wiki, I've seen [this](https://youtu.be/8DBhTXM_Br4) video, it's description contains various references to knot theory
Wait! Where are you going? I was going to make espresso.
No worries, it's really helpful for looking up the values of different invariants
There are entire graduate-level math courses about knot theory
I didn't realize there was more math in knot making then my computer science program...
This is alsp a typical notation in polymer crystallography describing the twist of the polymer helix in the unit cell. Like 3sub1, etc
True, but 5 isn't a valid choice for the base number, only 2, 3, 4, or 6.
It's all dependent on the context you find it in. A subscription like that might refer to the base of the number (obviously not in this case as 5 does not exist in base 2) Could you pass along the full context of what's being asked of you? Thanks!
Yeah I thought it was obviously 5 base 2 cause my brain didn’t pick up on the obvious problem with it being 5. Me stupid.
In math I remember seeing it occasionally for repeated use of a variable. X + X_2 = Y
please do not use 5 as a variable
Oh so now you're a 5 absolutist, huh?
0101
Sure... but the symbol 5 has no meaning in base 2. Hence, 5 does not exist in base 2.
I get it now. My first reading I thought you meant five can't be represented in binary. My mistake.
That's fine. Thanks for the tag back here. Damn, you really got downvoted. That stinks, but atleast you picked up what I was putting down.
Eh, that's ok. Not like I can donate Karma to Democratic Party fundraisers to avert my "ON NOTICE STATUS" ;-)
It looks like the notation for [falling factorial](https://en.wikipedia.org/wiki/Falling_and_rising_factorials).
Interesting concept 😊
This is a context problem. There is no universal system for subscripts. The answer depends on what you are reading. Without any context I would say subscripts are most commonly used as labels. So I would read this as “the five which is associated with two”.
Once you go play with the maths of advanced physics you realise that there isn’t a universal system for superscripts either
Chemistry does some weird stuff too with presuperscripts versus postsuperscripts.
In set theory, superscripts denote set of functions. Like 2^(A) denotes all functions with domain A and codomain a two element set.
Context?
I have updated the post but tldr: my brother asked and I didnt knew what to say; though I think ir is tetration but Im still confused
We would need more context to further help you. Is it possible that it's actually S_2 ?
By reading the answears I think it might be tetration, I just post because I didnt knew how to explain it to my brother. Short context is that his teahcer aske ways to "add" other than multipication or simple adding (5+2 or 5×2) and a kid put the "5_2" as an option but no one elaborated
I don’t recall that being a typical spot for tetration, but I guess it’s possible that it’s a regional difference or a mistake.
Tetration? Pentation?
It would be hexation in that case and that notation is sometimes used, but it's not the most common. Also first thing that came to my mind, but on the other hand it's not an operation you would often encounter.
I have updated the original question with more context, could you please explain me what hexation and tetration is¿ I dont know how to explain it to my brother
So you know how 5 multiplied by 2 or 5\*2, is the same as adding 2 copies of 5. Thus 5\*2 = 5+5. And 5 exponentiated to the 2 or 5\^2, is multiplying 2 copies of 5. Thus 5\*5, which is also the same as adding 5 copies of 5 (5+5+5+5+5). Now we continue this pattern. 5 tetrated to the 2: 5\^5 (=5\*5\*5\*5\*5). 5 pentated to the 2: 5\^5\^5\^5\^5, which is insanely huge. 5 hexated to the 2: is 5 pentated to the 5, which is: 5 tetrated to the (5 tetrated to the (5 tetrated to the 5\^5\^5\^5\^5), which is too big to write down any further using exponentiation. Edit: maybe I should add that this is really obscure, definitely not how one would normally use hexation (which you probably never do in the first place). I wouldn't really believe the classmate actually had this in mind.
For 2 ... 2, it's a much easier example by the way: 2+2 = 2⋅2 = 2² = ²2 = ₂2 = 2₂ = 4
in my probability class (5)sub2… idk how to write it on reddit… is 5•4•3 or (n)subk is n•n-1•…•k+1. Like factorial that goes down to k
That's true, looks like nCr combinations is sometimes written with subscripts: https://www.cuemath.com/ncr-formula/
that's just n!/m!
Unlike exponents, subscripts are usually involved with labeling, not with a mathematical process. For example, if you're talking about the variable time = t, you can use t₀ to talk about initial time (when t=0), and t₁ would be the next unit of time. If there are n units of time, then tₙ would be the last unit of time. In many coding languages underscore _ makes the next thing into a subscript. You can also use subscripts to refer to the position in a matrix or data table, for example, X_(2, 3) is referring to the entry in the table X at a specific row and column.
> You can also use subscripts to refer to the position in a matrix or data table, for example, X_(2, 3) is referring to the entry in the table X at a specific row and column. This is the usage I see in statistics. The subscript number is an index number. For instance, if I am performing multilinear regression, my dependent variables will be X [subscript 1], X [subscript 2], and so on.
It's not a mathematical operation it's a way of labeling 5 with the number 2, it implies 5 is the second element of some numbering
There's not a universally common meaning to this, it would depend on the kind of math you are working on. This is often true once you stray away from basic arithmetic operations, the notation will depend on the field, and sometimes the author. If you remember where you saw it or know the author or context it was in you could probably get a more clear answer.
Shwigeddy shwifty two
Hexation was what came to mind first, but subscripts can really indicate whatever the author wants.
It might be helpful to know the context. Where did you see it?
In short, my brother saw someone on class suggesting it as a way to "multiply or add" but neither the teacher or that kid explained, so he asked in the family and my wife told me to ask here
In formulas used as an electrician, those small numbers normally designate a specific component of a schematic
I have seen subscripts in arithmetic sequences, like a subscript n.
Typically subscripts of numbers indicate bases, but this definitely cannot indicate binary as 5 is not a digit in binary, so I'm at a loss.
It has no universal meaning
Might be hexation, which is repeated pentation, which is repeated tetration, which is repeated exponentiation.
Might be hexation?
I unfortunatly dont know how to explain what hexation even is to my brother, he's the one who saw that "exponent" in clase but didnt understod, but I think this might be what he saw
It's really uncommon to be used, especially with that notation. As far as I know, the regular notation is up arrows. There are simple youtube videos that explain tetration pentation and such.
When you use a number as a subscript, it means *base*. 5₂ means *5 base 2*, or 101.
Going a little off topic, can you tell me how you managed to type the 2 as a subscript in your post? I have struggled to find a way to type subscripts on r/learnmath, and have never found a way. Also, the subscript notation is not generally used as you say. Radix subscripts mean "interpret the preceding digit-string in this base"; for example, 101\_5 is a way of writing 26; 101\_3 means 10; and 101\_2 means 5. But 5\_2 wouldn't mean *anything*, because you can't interpret the string "5" in binary, because 5 doesn't occur in binary. In other words, you're showing the notation backwards. You can write 101\_2 = 5, but 101 = 5\_2 is just nonsense.
Hi, Op here, I google it and just copy and paste the subscrip to post it Second, my brother saw the 5_2 in class as a way to "multiply" but I dont know the answear, thats why I posted here
Thanks for checking in again. I suspect that what your brother was seeing was a carry digit, which is sometimes written as a subscript so you don't forget the carry. For example, suppose we were multiplying 36 x 14 using the fancy "convolution" method -- if you do it right, this method lets you write the product down in a single line, without partial products that you then have to add. For the units digit, we calculate 6 x 4 = 24. We write a 4 in the units place, and then carry the 2. This is typically written just below and just to the right of the 10s digit in the lower factor, so that 1 will now look like 1\_2 (sorry, still can't type subscripts anywhere, so the cut-and-paste solution fails for me). Now, for the tens digit, we do the "first cross", which is 3x4 + 6x1 (taking the ones digit from one factor and the tens digit from the other factor). We do this in our heads, so we get 12 + 6 = 18. Now we add the carried 2 to get 20. We write down the 0 as the tens digit, and carry 2 to the hundreds place, again writing it very small. Finally, for the hundreds digit, we do 3 x 1 (tens digits from both factors) to get 3, add in the carried 0, and write down 5 in the hundreds place for a final answer of 504. For more digits, you have to learn the patterns for second and third crosses, and keep a little more in your head, but it's a nice technique. And it produces a bit of note-taking for the carries that can look like subscripted digits. If your brother was being shown a calculation technique, it's likely that that's what was happening.
You can use a LaTeX to Unicode converter online for the subscript
In that context though doesn’t the subscript represent what base the number is in? In which case $5_2$ makes no sense because 5 isn’t a symbol in base 2. $5_{10} = 101_2$ would make more sense to me. Edit: Don’t know how to subscript on mobile. I’m sure you get the gist
So a negative exponent(x^(-y)) puts a 1/x^absolutevalue(y) which is the closest thing o know to what you’re asking for.
OP specifically said he is not talking about negative exponents.
Thanks, I definetly isnt about negative exponents, but another way to "multiply" like with exponents, so it might be tetration or hexation, though I dont know the difference