Question

What is the missing number from this number sentence?

7 ? 14 31

I'm always confused with this.

Answer 1

9

9 = 7+(2^0+1)
14 = 9+(2^2+1)
31 = 14+(2^4+1)
Then nth term is clearly 7 + 2^(2n-2)+1

That is only one of many ways to fill in the hole. You have so little to work with, you are free to pick almost any value you choose.

I suspect that my solution is not the one intended, since you are evidently new at this, so the sequence must be fairly simple. But the growth from 7 to 14 over two terms is so small compared to the growth from 14 to 31 in a single jump, it's hard to say.

You might say
7+0=7
7+7=14
14+17=31
31+27=58
and so on