A001251(n)/2.

Terms

a(0) =0a(1) =0a(2) =1a(3) =6a(4) =35a(5) =221a(6) =1554a(7) =12108a(8) =104293a(9) =986452a(10) =10186669a(11) =114173261a(12) =1381606490a(13) =17963133122a(14) =249838334627