This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A216628 #4 Sep 19 2012 02:23:14 %S A216628 1,1,1,2,3,18,60,1200,10500,735000,18522000,4667544000,359400888000, %T A216628 332086420512000,81408613942656000,279394363051195392000, %U A216628 224737840779305293440000,2892376010829659126572800000,7812628980363223707442752000000,379850021025259936655866602240000000 %N A216628 a(n) = A163085(n)/n!. %o A216628 (Sage) %o A216628 def A216628(n): %o A216628 swing = lambda n: factorial(n)/factorial(n//2)^2 %o A216628 A163085 = lambda n: mul(swing(i) for i in (0..n)) %o A216628 return A163085(n)/factorial(n) %o A216628 [A216628(n) for n in (0..19)] %Y A216628 Cf. A056040. %K A216628 nonn %O A216628 0,4 %A A216628 _Peter Luschny_, Sep 18 2012