1 + 12*n + 81*n^3 + n*(105*n + 81*n^3)/2.

Terms

a(0) =1a(1) =187a(2) =1531a(3) =5977a(4) =16441a(5) =36811a(6) =71947a(7) =127681a(8) =210817a(9) =329131a(10) =491371a(11) =707257a(12) =987481a(13) =1343707a(14) =1788571a(15) =2335681a(16) =2999617a(17) =3795931a(18) =4741147a(19) =5852761a(20) =7149241a(21) =8650027a(22) =10375531a(23) =12347137a(24) =14587201a(25) =17119051a(26) =19966987a(27) =23156281a(28) =26713177