a(n) = A289676(3*n+1).

Terms

a(0) =2a(1) =2a(2) =4a(3) =5a(4) =10a(5) =21a(6) =43a(7) =85a(8) =146a(9) =250a(10) =462a(11) =960a(12) =2069a(13) =4296a(14) =8485a(15) =16496a(16) =32041a(17) =61700a(18) =118357