a(n) = (6*n + 3)^6.

Terms

a(0) =729a(1) =531441a(2) =11390625a(3) =85766121a(4) =387420489a(5) =1291467969a(6) =3518743761a(7) =8303765625a(8) =17596287801a(9) =34296447249a(10) =62523502209a(11) =107918163081a(12) =177978515625a(13) =282429536481a(14) =433626201009a(15) =646990183449a(16) =941480149401