a(n) = binomial(n+7,7)*binomial(n+7,6)/(n+7).

Terms

a(0) =1a(1) =28a(2) =336a(3) =2520a(4) =13860a(5) =60984a(6) =226512a(7) =736164a(8) =2147145a(9) =5725720a(10) =14158144a(11) =32821152a(12) =71954064a(13) =150233760a(14) =300467520a(15) =578399976a(16) =1075994073a(17) =1941008916a(18) =3405278800a(19) =5824819000a(20) =9735768900a(21) =15931258200a(22) =25565576400a(23) =40293571500a(24) =62455035825a(25) =95315993136