a(n) = A036800(n)/2.

Terms

a(0) =0a(1) =1a(2) =9a(3) =45a(4) =173a(5) =573a(6) =1725a(7) =4861a(8) =13053a(9) =33789a(10) =84989a(11) =208893a(12) =503805a(13) =1196029a(14) =2801661a(15) =6488061a(16) =14876669a(17) =33816573a(18) =76283901a(19) =170917885a(20) =380633085a(21) =843055101a(22) =1858076669a(23) =4076863485a(24) =8908701693a(25) =19394461693a(26) =42077257725a(27) =90999619581a(28) =196226318333