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 A205958 #9 Mar 30 2012 17:27:13 %S A205958 1,1,1,1,2,2,3,3,48,16,40,40,270,270,945,63,129024,129024,64512,64512, %T A205958 2016000,96000,528000,528000,144342000,28868400,187644600,20849400, %U A205958 1787836050,1787836050,59594535,59594535,3999321544458240,121191561953280,1030128276602880 %N A205958 a(0) = 1 and a(n) = A180000(n)*a(floor(n/2))^2 for n > 0. %C A205958 lcm(1,2,..,n) = (n!*a(n)) / ((n/2)!*a(n/2))^2. %C A205958 lcm(1,2,..,n)*a(n) is a divisor of n! and n!/(lcm(1,2,..,n)*a(n)) is a square. %o A205958 (Sage) %o A205958 def A205958(n) : %o A205958 if n == 0 : return 1 %o A205958 return A180000(n)*A205958(n//2)^2 %Y A205958 Cf. A180000, A025527, A205959. %K A205958 nonn %O A205958 0,5 %A A205958 _Peter Luschny_, Feb 04 2012