a(n) = Sum_{d|n} d^(3*n/d - 2).

Terms

a(0) =1a(1) =3a(2) =4a(3) =21a(4) =6a(5) =216a(6) =8a(7) =1289a(8) =2197a(9) =8828a(10) =12a(11) =142278a(12) =14a(13) =526704a(14) =1672464a(15) =5246993a(16) =18a(17) =76887669a(18) =20a(19) =345319966a(20) =1163085032a(21) =2147498312a(22) =24a(23) =52918480178a(24) =1220703151a(25) =137438982060a(26) =847293392440a(28) =30a(30) =32