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

Terms

a(0) =1a(1) =3a(2) =15a(3) =91a(4) =333a(5) =891a(6) =1963a(7) =3795a(8) =6681a(9) =10963a(10) =17031a(11) =25323a(12) =36325a(13) =50571a(14) =68643a(15) =91171a(16) =118833a(17) =152355a(18) =192511a(19) =240123a(20) =296061a(21) =361243a(22) =436635a(23) =523251a(24) =622153a(25) =734451a(26) =861303a(27) =1003915a(28) =1163541a(29) =1341483