Răspuns:
10,11,12,13,20,21,22,30,31,40
Explicație pas cu pas:
ab<sau egal 4=>1+0=1<sau egal 4=>a=1,b=0=>ab=10
=>1+1=2< sau egal 4=>a=1,b=2=>ab=11
=>1+2=3 < sau egal 4=>a=1,b=2=>ab=12
=>1+3=4< sau egal 4=>a=1,b=3=>ab=13
=>2+0=2< sau egal 4=>a=2,b=0=>ab=20
=>2+1=3< sau egal 4=>a=2,b=1=>ab=21
=>2+2=4< sau egal 4=>a=2,b=2=>ab=22
=>3+0=3< sau egal 4=>a=3,b=0=>ab=30
=>3+1=4< sau egal 4=>a=3,b=1=>ab=31
=>4+0=4< sau egal 4=>a=3,b=1=>ab=40
