%I #4 Sep 19 2012 02:23:14

%S 1,1,1,2,3,18,60,1200,10500,735000,18522000,4667544000,359400888000,

%T 332086420512000,81408613942656000,279394363051195392000,

%U 224737840779305293440000,2892376010829659126572800000,7812628980363223707442752000000,379850021025259936655866602240000000

%N a(n) = A163085(n)/n!.

%o (Sage)

%o def A216628(n):

%o swing = lambda n: factorial(n)/factorial(n//2)^2

%o A163085 = lambda n: mul(swing(i) for i in (0..n))

%o return A163085(n)/factorial(n)

%o [A216628(n) for n in (0..19)]

%Y Cf. A056040.

%K nonn

%O 0,4

%A _Peter Luschny_, Sep 18 2012