Dirichlet g.f.: Product_{k>=2} (1 + k^(-s))^(3^(k-1)).

Terms

a(0) =1a(1) =3a(2) =9a(3) =30a(4) =81a(5) =270a(6) =729a(7) =2269a(8) =6597a(9) =19926a(10) =59049a(11) =178146a(12) =531441a(13) =1596510a(14) =4783698a(15) =14355900a(16) =43046721a(17) =129162141a(18) =387420489a(19) =1162322946a(20) =3486790962a(21) =10460530350a(22) =31381059609a(23) =94143737979a(24) =282429539721a(25) =847290203766