a(n) = 3*(2*n - 1)*( 3*(2*n - 1)^3 - 1) / 2 for n > 0.

Terms

a(0) =3a(1) =360a(2) =2805a(3) =10794a(4) =29511a(5) =65868a(6) =128505a(7) =227790a(8) =375819a(9) =586416a(10) =875133a(11) =1259250a(12) =1757775a(13) =2391444a(14) =3182721a(15) =4155798a(16) =5336595a(17) =6752760a(18) =8433669a(19) =10410426a(20) =12715863a(21) =15384540a(22) =18452745a(23) =21958494a(24) =25941531a(25) =30443328a(26) =35507085a(27) =41177730a(28) =47501919a(29) =54528036