a(n) = (3*n-1)*(n^4-18*n^3+179*n^2-582*n+720)/120.

Terms

a(0) =5a(1) =6a(2) =12a(3) =33a(4) =77a(5) =153a(6) =274a(7) =460a(8) =741a(9) =1160a(10) =1776a(11) =2667a(12) =3933a(13) =5699a(14) =8118a(15) =11374a(16) =15685a(17) =21306a(18) =28532a(19) =37701a(20) =49197a(21) =63453a(22) =80954a(23) =102240a(24) =127909a(25) =158620a(26) =195096a(27) =238127a(28) =288573a(29) =347367