a(n) = ceiling(n^4/4).

Terms

a(0) =0a(1) =1a(2) =4a(3) =21a(4) =64a(5) =157a(6) =324a(7) =601a(8) =1024a(9) =1641a(10) =2500a(11) =3661a(12) =5184a(13) =7141a(14) =9604a(15) =12657a(16) =16384a(17) =20881a(18) =26244a(19) =32581a(20) =40000a(21) =48621a(22) =58564a(23) =69961a(24) =82944a(25) =97657a(26) =114244a(27) =132861a(28) =153664a(29) =176821