a(n) = (4*n^4 - 4*n^3 - n^2 + 3*n)/2.

Terms

a(0) =1a(1) =17a(2) =108a(3) =382a(4) =995a(5) =2151a(6) =4102a(7) =7148a(8) =11637a(9) =17965a(10) =26576a(11) =37962a(12) =52663a(13) =71267a(14) =94410a(15) =122776a(16) =157097a(17) =198153a(18) =246772a(19) =303830a(20) =370251a(21) =447007a(22) =535118a(23) =635652a(24) =749725a(25) =878501a(26) =1023192a(27) =1185058a(28) =1365407a(29) =1565595