Twice the median of {Stirling2(n, k), k = 0..n}.

Terms

a(0) =1a(1) =2a(2) =2a(3) =2a(4) =11a(5) =30a(6) =84a(7) =254a(8) =717a(9) =1500a(10) =13035a(11) =44550a(12) =300950a(13) =1505504a(14) =3854579a(15) =14283372a(16) =83480149a(17) =251709276a(18) =3136016690a(19) =12605049160a(20) =162391467080a(21) =691231886400