a(n) = binomial(n+3,3)*binomial(n+6,6).

Terms

a(0) =1a(1) =28a(2) =280a(3) =1680a(4) =7350a(5) =25872a(6) =77616a(7) =205920a(8) =495495a(9) =1101100a(10) =2290288a(11) =4504864a(12) =8446620a(13) =15193920a(14) =26356800a(15) =44279424a(16) =72299997a(17) =115079580a(18) =179012680a(19) =272734000a(20) =407737330a(21) =599124240a(22) =866502000a(23) =1235052000a(24) =1736791875a(25) =2412056556a(26) =3311225568a(27) =4496726080a(28) =6045343480