a(n) = (n^8 + n^4)/2.

Terms

a(0) =0a(1) =1a(2) =136a(3) =3321a(4) =32896a(5) =195625a(6) =840456a(7) =2883601a(8) =8390656a(9) =21526641a(10) =50005000a(11) =107186761a(12) =215001216a(13) =407879641a(14) =737913736a(15) =1281470625a(16) =2147516416a(17) =3487920481a(18) =5510032776a(19) =8491846681a(20) =12800080000a(21) =18911526921a(22) =27438053896a(23) =39155632561a(24) =55037822976