(A192251)/2.

Terms

a(0) =0a(1) =1a(2) =4a(3) =24a(4) =129a(5) =759a(6) =4455a(7) =26763a(8) =161898a(9) =988438a(10) =6069228a(11) =37460952a(12) =232160184a(13) =1443830084a(14) =9005809184a(15) =56316652784a(16) =352949825249