Respuesta :

AL2006
I tried to think of a fancy formula for it, then decided it's just easier to list them:

1
2
3
11
12
13
21
22
23

That's 9 of them.
markopolo
there are 9 numbers that are positive integers that can be formed by the #s 1,2,&3 THAT R LESS THAN 25 1 2 3 11 12 13 21 22 23