I think that the number that would complete the number sequence is 38. My reasoning is that as the numbers increase, there is a sort of pattern to them. 3 goes to 8, increasing by 5. 8 goes to 14, increasing by 6. 12 goes to 21, increasing by 7. 21 increases to 29 by 8, so logically, 29 would increase to 38 by 9, following the current pattern of increase.
