a(n) = 7*3^n + 1.

Terms

a(0) =8a(1) =22a(2) =64a(3) =190a(4) =568a(5) =1702a(6) =5104a(7) =15310a(8) =45928a(9) =137782a(10) =413344a(11) =1240030a(12) =3720088a(13) =11160262a(14) =33480784a(15) =100442350a(16) =301327048a(17) =903981142a(18) =2711943424a(19) =8135830270a(20) =24407490808a(21) =73222472422a(22) =219667417264a(23) =659002251790