a(n) = 10^n + 5.

Terms

a(0) =6a(1) =15a(2) =105a(3) =1005a(4) =10005a(5) =100005a(6) =1000005a(7) =10000005a(8) =100000005a(9) =1000000005a(10) =10000000005a(11) =100000000005