Third convolution of the powers of 3 (A000244).

Terms

a(0) =1a(1) =9a(2) =54a(3) =270a(4) =1215a(5) =5103a(6) =20412a(7) =78732a(8) =295245a(9) =1082565a(10) =3897234a(11) =13817466a(12) =48361131a(13) =167403915a(14) =573956280a(15) =1951451352a(16) =6586148313a(17) =22082967873a(18) =73609892910a(19) =244074908070a(20) =805447196631