a(n) = Sum_{d|n} d * 3^(n-d).

Terms

a(0) =1a(1) =5a(2) =12a(3) =49a(4) =86a(5) =492a(6) =736a(7) =3977a(8) =8757a(9) =34030a(10) =59060a(11) =384924a(12) =531454a(13) =2672528a(14) =6672552a(15) =26093113a(16) =43046738a(17) =261646137a(18) =387420508a(19) =2181624374a(20) =4682526672a(21) =17435870644a(22) =31381059632a(23) =204908769276a(24) =299863458511