a(n) = (4*n^3 - 6*n^2 + 20*n + 3)/3.

Terms

a(0) =1a(1) =7a(2) =17a(3) =39a(4) =81a(5) =151a(6) =257a(7) =407a(8) =609a(9) =871a(10) =1201a(11) =1607a(12) =2097a(13) =2679a(14) =3361a(15) =4151a(16) =5057a(17) =6087a(18) =7249a(19) =8551a(20) =10001a(21) =11607a(22) =13377a(23) =15319a(24) =17441a(25) =19751a(26) =22257a(27) =24967a(28) =27889a(29) =31031