a(n) = (5n+3)^6.

Terms

a(0) =729a(1) =262144a(2) =4826809a(3) =34012224a(4) =148035889a(5) =481890304a(6) =1291467969a(7) =3010936384a(8) =6321363049a(9) =12230590464a(10) =22164361129a(11) =38068692544a(12) =62523502209a(13) =98867482624a(14) =151334226289a(15) =225199600704a(16) =326940373369