a(n) = (4*n^3 - 6*n^2 + 14*n + 3)/3.

Terms

a(0) =1a(1) =5a(2) =13a(3) =33a(4) =73a(5) =141a(6) =245a(7) =393a(8) =593a(9) =853a(10) =1181a(11) =1585a(12) =2073a(13) =2653a(14) =3333a(15) =4121a(16) =5025a(17) =6053a(18) =7213a(19) =8513a(20) =9961a(21) =11565a(22) =13333a(23) =15273a(24) =17393a(25) =19701a(26) =22205a(27) =24913a(28) =27833a(29) =30973