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

Terms

a(0) =1a(1) =7a(2) =27a(3) =76a(4) =175a(5) =351a(6) =637a(7) =1072a(8) =1701a(9) =2575a(10) =3751a(11) =5292a(12) =7267a(13) =9751a(14) =12825a(15) =16576a(16) =21097a(17) =26487a(18) =32851a(19) =40300a(20) =48951a(21) =58927a(22) =70357a(23) =83376a(24) =98125a(25) =114751a(26) =133407a(27) =154252a(28) =177451a(29) =203175