a(n) = n^5*(n^4 + 1)/2.

Terms

a(0) =0a(1) =1a(2) =272a(3) =9963a(4) =131584a(5) =978125a(6) =5042736a(7) =20185207a(8) =67125248a(9) =193739769a(10) =500050000a(11) =1179054371a(12) =2580014592a(13) =5302435333a(14) =10330792304a(15) =19222059375a(16) =34360262656a(17) =59294648177a(18) =99180589968a(19) =161345086939a(20) =256001600000