abcde:cde= ab+1, rest ab+72
abcde=cde•(ab+1)+ab+72
ab•1000+cde=ab•cde+cde+ab+72 /-cde
ab•1000=ab(cde+1)+72
ab(1000-cde-1)=72
ab(999-cde)=72; ab e nr de doua cifre
72=72•1=36•2=24•3=18•4=12•6
ab=72 si 999-cde=1 => cde=998
ab=36 si 999-cde=2 => cde=997
ab=24 si 999-cde=3=> cde=996
ab=18 si 999-cde=4=> cde=995
ab=12 si 999-cde=6=> cde=993
abcde={12993; 18995; 24996; 36997; 72998}
