what number comes next 3 4 6 9 13 18 24
31 - as the difference (starting from 1) increases by 1so:3,+1=4,+2=6,+3=9,+4=13,+5=18,+6=24,+7=31,
31.3+1=44+2=66+3=99+4=1313+5=1818+6=2424+7=31