Sum_{0<j<n} (n^4-j^4).

Terms

a(0) =15a(1) =145a(2) =670a(3) =2146a(4) =5501a(5) =12131a(6) =23996a(7) =43716a(8) =74667a(9) =121077a(10) =188122a(11) =282022a(12) =410137a(13) =581063a(14) =804728a(15) =1092488a(16) =1457223a(17) =1913433a(18) =2477334a(19) =3166954a(20) =4002229a(21) =5005099a(22) =6199604a(23) =7611980a(24) =9270755a(25) =11206845a(26) =13453650a(27) =16047150