Răspuns :
d:i=c si r si r<i si r=c
d:25=c conform teoremei impartirii cu rest⇒d=25·r+r⇒d=26·r dar r<25
luam cazurile
r=0⇒d=0 caz imposibil
r=1⇒d=26·1=26 nu merge <500
r=2⇒d=26·2=52 nu merge <500
......................
r=19⇒d=26·19=494 nu merge <500
r=20⇒d=26·20=520
r=21⇒d=26·21=546
r=22⇒d=26·22=572
r=23⇒d=26·23=598
r=24⇒d=26·24=624
d:25=c conform teoremei impartirii cu rest⇒d=25·r+r⇒d=26·r dar r<25
luam cazurile
r=0⇒d=0 caz imposibil
r=1⇒d=26·1=26 nu merge <500
r=2⇒d=26·2=52 nu merge <500
......................
r=19⇒d=26·19=494 nu merge <500
r=20⇒d=26·20=520
r=21⇒d=26·21=546
r=22⇒d=26·22=572
r=23⇒d=26·23=598
r=24⇒d=26·24=624
n = 25c +r r=c r < 25 n = 25r + r = 26r 26r > 500 ⇒r≥20 ⇒ r∈{20,21,22,23,24} ⇒n∈{520,546,572,598,624}