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

Terms

a(0) =1a(1) =2a(2) =8a(3) =40a(4) =137a(5) =356a(6) =772a(7) =1478a(8) =2585a(9) =4222a(10) =6536a(11) =9692a(12) =13873a(13) =19280a(14) =26132a(15) =34666a(16) =45137a(17) =57818a(18) =73000a(19) =90992a(20) =112121a(21) =136732a(22) =165188a(23) =197870a(24) =235177a(25) =277526a(26) =325352a(27) =379108a(28) =439265a(29) =506312