a(n) = N(7,n), where N(7,x) is the 7th Narayana polynomial.

Terms

a(0) =1a(1) =429a(2) =4279a(3) =20071a(4) =65445a(5) =171481a(6) =387739a(7) =788019a(8) =1476841a(9) =2596645a(10) =4335711a(11) =6936799a(12) =10706509a(13) =16025361a(14) =23358595a(15) =33267691a(16) =46422609a(17) =63614749a(18) =85770631a(19) =113966295a(20) =149442421a(21) =193620169a(22) =248117739a(23) =314767651