What is the name for a number plus itself?

Question

I'm asking out of curiosity more than anything else. A number multiplied by itself is squared, is there a specific mathematical term for a number plus itself?

$(n*n = n^2, n+n=?)$

Answer 1

Written mathematically, one has

$$n\times n=n^2,n+n=2n$$

Reading the above with words, one would put the words "symbol by symbol", so this would be read

$$\text{n (pronounced en) times n equals n squared, n plus n equals two n}$$

Sometimes even the implicit symbols are read, so "two n" can be replaced by "two times n".

There are alternatives for "two n" such as "n doubled" or "twice n" (I credit @Hurkyl's answer), which are commonly used, though I would say these are even more useful when going from text to math (rather than in the other direction).

For example, if a problem states "my neighbour's garden is twice as big as my garden", then if the size of my garden is $n$, the size of my neighbour's garden will be $2n$.

The word "twice" is specific for 2, but there are words analogous to "double" for many other numbers, i.e., "triple" for 3, "quadruple" for 4, "octuple" for 8, etc., and mathematicians even use "$n$-uple" for $n$ or whatever letter they need.

Outside mathematics one finds the words ended in -fold like "twofold","threefold","tenfold",etc. These are adjectives, so one can talk about a "tenfold increase in the use of chemical products"

Answer 2

You square $n$ or you double $n$.

For one, the result is $n$ squared. For the other, we would usually just say $2n$ -- that is, two en -- I don't think I've ever heard anyone say that it is twice $n$ or $n$ doubled, although those would be understood.

If you had a specific number, though, I think I've heard phrases like "twice twenty-five" before, although "twenty-five times two" is probably more common.