a(n) = 6*5^n+1.

Terms

a(0) =7a(1) =31a(2) =151a(3) =751a(4) =3751a(5) =18751a(6) =93751a(7) =468751a(8) =2343751a(9) =11718751a(10) =58593751a(11) =292968751a(12) =1464843751a(13) =7324218751a(14) =36621093751a(15) =183105468751a(16) =915527343751