a(n) = n*(5*n^2-8*n+5)/2.

Terms

a(0) =0a(1) =1a(2) =9a(3) =39a(4) =106a(5) =225a(6) =411a(7) =679a(8) =1044a(9) =1521a(10) =2125a(11) =2871a(12) =3774a(13) =4849a(14) =6111a(15) =7575a(16) =9256a(17) =11169a(18) =13329a(19) =15751a(20) =18450a(21) =21441a(22) =24739a(23) =28359a(24) =32316a(25) =36625a(26) =41301a(27) =46359a(28) =51814a(29) =57681