a(n) = (4*n + 3)^6.

Terms

a(0) =729a(1) =117649a(2) =1771561a(3) =11390625a(4) =47045881a(5) =148035889a(6) =387420489a(7) =887503681a(8) =1838265625a(9) =3518743761a(10) =6321363049a(11) =10779215329a(12) =17596287801a(13) =27680640625a(14) =42180533641a(15) =62523502209a(16) =90458382169a(17) =128100283921a(18) =177978515625a(19) =243087455521a(20) =326940373369a(21) =433626201009a(22) =567869252041