Răspuns :
1,3,2,6,9,4,12,5,15,6,18,7,21,8,24,9,27,10,30,11,33,12,36,13,39...............
daca te uiti din 2 in 2 cifre, vei vedra regula
123
369
deci sirul va fi
1 3 2 6 3 9 4 12 5 15 6 18 7 21 etc
123
369
deci sirul va fi
1 3 2 6 3 9 4 12 5 15 6 18 7 21 etc