abc:bc=6 rest 5
=> abc=6bc+5
100a+bc=6bc+5
100a=6bc-bc+5
100a=5bc+5 /:5
20a=bc+1
20a=10b+c+1
=> c=9
deci, 20a=10b+10
2a=b+1
pentru a=1 =>b=1; abc=119
a=2=> b=3; abc=239
a=3 => b=5; abc=359
a=4=> b=7; abc=479
a=5=> b=9; abc=599
abc∈{119, 239, 359, 479, 599}
