Find the missing term in the given series.

Question

1,3,7,?,121,721

Answer 1

I see a relationship between 3, 7, ?, 121, 721 but not with the first term of 1 !?!?

3*3-2=9-2=7

4*7-3=28-3=25

5*25-4=125-4=121

6*121-5=726-5=721

so ?=25