a(n) = binomial(n,15).

Terms

a(0) =1a(1) =16a(2) =136a(3) =816a(4) =3876a(5) =15504a(6) =54264a(7) =170544a(8) =490314a(9) =1307504a(10) =3268760a(11) =7726160a(12) =17383860a(13) =37442160a(14) =77558760a(15) =155117520a(16) =300540195a(17) =565722720a(18) =1037158320a(19) =1855967520a(20) =3247943160a(21) =5567902560a(22) =9364199760a(23) =15471286560a(24) =25140840660a(25) =40225345056a(26) =63432274896