I will say the answer is 125
Each of them has a power of thirds
So it goes like this:
1 to the power 3 = 1
2 to the power 3 = 8
3 to the power 3 = 27
4 to the power 3 = 64
5 to the power 3 = 125
And I think this is one of the IQ test questions..haha
Hope this helped you =)