a(n) = A192809(n)/2.

Terms

a(0) =0a(1) =0a(2) =1a(3) =7a(4) =37a(5) =183a(6) =893a(7) =4351a(8) =21205a(9) =103367a(10) =503917a(11) =2456655a(12) =11976517a(13) =58387095a(14) =284644701a(15) =1387679903a(16) =6765119669a(17) =32980836455a(18) =160785858381a(19) =783851928559