Numbers Puzzle

[johnny7]

Came across this numbers puzzle which is annoying the hell out of me. Can anyone work it out?

1 = -7
2 = 0
3 = 73
4 = 1016
5 = ?
6 = ?
etc

[Geoff13]

5=15617
first is 8 less than 1 to the power of 2
second is 8 less than 2 to the power of 3
third is 8 less than 3 to the power of 4
fourth is 8 less than 4 to the power of 5
so fifth is 8 less than 5 to the power of 6
and sixth will be 8 less than 6 to the power of 7....

[johnny7]

Nice one. Where did you even begin to work that one out?

[Geoff13]

I added 8 to all the numbers (to change the -7 to 1) and recognised the resulting numbers as powers. A quick bit of experimenting led to the pattern. I have to own up to being a recently retired maths teacher!!

[johnny7]

Ah ok. Well thanks. I was pretty close to eating some fruit if I didn't solve that problem.