n=13xC+r
Î =13 => r maxim 12
r=2C =>C=r:2, deci restul este par si maxim 12
n=13xC+2C
n=15C
r=2 => C=1 => n=1x15
r=4=>C=2 => n=2x15=30
r=6 => C=3 => n=3x15=45
r=8 => C=4 => n=4x15=60
r=10 => C=5 => n=5x15=75
r=12 => C=6 => n=6x15=90
n=15,30,45,60,75,90