There are infinitely many ways.
Think of any number, say x.
calculate y = 13 - x
Then x + y = 13
Since the choice of x was arbitrary, there are infinitely many answers.
That applies to pairs of numbers. You can repeat the process for sums of 3, 4, ... numbers.
Also, you can look at multiplication and other ways of combining numbers (binary operations).
There are no two WHOLE NUMBERS that equal 13 besides the obvious 1 & 13.
13 and 3
1 x 13 and 13 x 1
They are: 13+7 = 20
17 and 13
There are no two WHOLE NUMBERS that equal 13 besides the obvious 1 & 13.
13*31=403 13 and 31 are prime numbers.
338
13 and 3
1 x 13 and 13 x 1
The numbers are 13 and 14.
2 and 13.
887 and 13
They are: 13+7 = 20
In whole numbers, 2. 1 * 13 = 13
They are: 13*13 = 169 or 167+2 = 169
7, 11 and 13.