a(n) = (n^2 + 1)*3^n.

Terms

a(0) =1a(1) =6a(2) =45a(3) =270a(4) =1377a(5) =6318a(6) =26973a(7) =109350a(8) =426465a(9) =1614006a(10) =5963949a(11) =21611934a(12) =77058945a(13) =271034910a(14) =942244893a(15) =3242852982a(16) =11063007297a(17) =37450647270a(18) =125911658925a(19) =420738651054