a(n) = 6*8^n+1.

Terms

a(0) =7a(1) =49a(2) =385a(3) =3073a(4) =24577a(5) =196609a(6) =1572865a(7) =12582913a(8) =100663297a(9) =805306369a(10) =6442450945a(11) =51539607553a(12) =412316860417