10^n + xy = 10000000000000000 .......000000 +
xy
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= 10000000000000 ..... 00000xy se divide cu 9
daca 1 + 0 + 0+ ...... + 0 + x + y = 1 +x +y este multiplu de 9
1 + x +y = 9
x + y = 9 - 1 = 8
17 ; 26 ; 35 ; 44 ; 53 ; 62 ; 71 ; 80
sau 1 + x +y =18
x + y =17
89 , 98