a(n) = (n^5-n-5)/5.

Terms

a(0) =-1a(1) =-1a(2) =5a(3) =47a(4) =203a(5) =623a(6) =1553a(7) =3359a(8) =6551a(9) =11807a(10) =19997a(11) =32207a(12) =49763a(13) =74255a(14) =107561a(15) =151871a(16) =209711a(17) =283967a(18) =377909a(19) =495215a(20) =639995a(21) =816815a(22) =1030721a(23) =1287263a(24) =1592519a(25) =1953119a(26) =2376269a(27) =2869775a(28) =3442067a(29) =4102223