a(n) = (4*n)^7.

Terms

a(0) =0a(1) =16384a(2) =2097152a(3) =35831808a(4) =268435456a(5) =1280000000a(6) =4586471424a(7) =13492928512a(8) =34359738368a(9) =78364164096a(10) =163840000000a(11) =319277809664a(12) =587068342272