a(n) = Stirling2(n, floor(n/2)).

Terms

a(0) =1a(1) =0a(2) =1a(3) =1a(4) =7a(5) =15a(6) =90a(7) =301a(8) =1701a(9) =7770a(10) =42525a(11) =246730a(12) =1323652a(13) =9321312a(14) =49329280a(15) =408741333a(16) =2141764053a(17) =20415995028a(18) =106175395755