a(n) = ((2*n+1)^3+(-1)^n)/2.

Terms

a(0) =1a(1) =13a(2) =63a(3) =171a(4) =365a(5) =665a(6) =1099a(7) =1687a(8) =2457a(9) =3429a(10) =4631a(11) =6083a(12) =7813a(13) =9841a(14) =12195a(15) =14895a(16) =17969a(17) =21437a(18) =25327a(19) =29659a(20) =34461a(21) =39753a(22) =45563a(23) =51911a(24) =58825a(25) =66325a(26) =74439a(27) =83187a(28) =92597a(29) =102689