a(n) = A289677(3*n+1).

Terms

a(0) =0a(1) =2a(2) =4a(3) =11a(4) =22a(5) =43a(6) =85a(7) =171a(8) =366a(9) =774a(10) =1586a(11) =3136a(12) =6123a(13) =12088a(14) =24283a(15) =49040a(16) =99031a(17) =200444a(18) =405931