xyz = 100x + 10y +z ,,,
........ cu x , y,z in baza 10 sunt x ,y ,z = 1,2,3,4.. 9
ex. ( 222x + 222y +222z) /144 = 222 ( x +y+z ) /144 = 37( x +y +z) / 24
ex . = numar natural daca x +y+ z = 24
x =9 ,y=7 ,z =8
x =9 y=8 z =7
x= 8 y =9 z=7
x=8 y=7 z = 9
x=7 y=8 z=9
x=7 y=9 z=8 sunt xyz cu cifre distincte
b. ( 10000x + 1000y +100y +10x +y - 100y) =
= ( 10010x + 1001y) = 13· 770 x + 13 ·77y =13· ( 770x + 77y)
ex. =13 ( 770x +77y) / 13 = ( 770x + 77y) ∈ N
