a(n) = 15*(n+1)*binomial(n+2,15)/2.

Terms

a(0) =105a(1) =1800a(2) =16320a(3) =104040a(4) =523260a(5) =2209320a(6) =8139600a(7) =26860680a(8) =80901810a(9) =225544440a(10) =588376800a(11) =1448655000a(12) =3389852700a(13) =7582037400a(14) =16287339600a(15) =33738060600a(16) =67621543875a(17) =131530532400a(18) =248917996800a(19) =459351961200a(20) =828225505800