a(n) = (4n+2)^7.

Terms

a(0) =128a(1) =279936a(2) =10000000a(3) =105413504a(4) =612220032a(5) =2494357888a(6) =8031810176a(7) =21870000000a(8) =52523350144a(9) =114415582592a(10) =230539333248a(11) =435817657216a(12) =781250000000