Numerator of Sum_{k=0..n} 1/k!!.

Terms

a(0) =1a(1) =2a(2) =5a(3) =17a(4) =71a(5) =121a(6) =731a(7) =1711a(8) =41099a(9) =370019a(10) =740101a(11) =2713789a(12) =1206137a(13) =423355111a(14) =846710651a(15) =1814380259a(16) =203210595443a(17) =12654139763a(18) =531473870981