a(n) = binomial(n,25).

Terms

a(0) =1a(1) =26a(2) =351a(3) =3276a(4) =23751a(5) =142506a(6) =736281a(7) =3365856a(8) =13884156a(9) =52451256a(10) =183579396a(11) =600805296a(12) =1852482996a(13) =5414950296a(14) =15084504396a(15) =40225345056a(16) =103077446706a(17) =254661927156a(18) =608359048206