a(n) = (7*n + 3)^6.

Terms

a(0) =729a(1) =1000000a(2) =24137569a(3) =191102976a(4) =887503681a(5) =3010936384a(6) =8303765625a(7) =19770609664a(8) =42180533641a(9) =82653950016a(10) =151334226289a(11) =262144000000a(12) =433626201009a(13) =689869781056