a(n) = 3*(n + 1)*(n + 2)*(3*n + 1)*(3*n + 4)/4.

Terms

a(0) =6a(1) =126a(2) =630a(3) =1950a(4) =4680a(5) =9576a(6) =17556a(7) =29700a(8) =47250a(9) =71610a(10) =104346a(11) =147186a(12) =202020a(13) =270900a(14) =356040a(15) =459816a(16) =584766a(17) =733590a(18) =909150a(19) =1114470a(20) =1352736a(21) =1627296a(22) =1941660a(23) =2299500a(24) =2704650a(25) =3161106a(26) =3673026a(27) =4244730a(28) =4880700a(29) =5585580