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 A213323 #6 Jun 09 2012 06:50:34
%S A213323 1,1,2,6,0,44,304,2568,26704,200240,1931616,20849696,246556672,
%T A213323 3300906816,46382446720,695413794944,11120648673024,188600719094528,
%U A213323 3394592207824384,64513420630110720,1290420198709682176,27102196040419214336,596237419436696543232,13713106494042086045696
%N A213323 Number of permutations of n objects such that no four-element subset is preserved.
%C A213323 The limit as n -> infinity of a(n)/n! = (13+9*exp(1/3))/(6*exp(25/12)) or approximately 0.5304422700.
%F A213323 E.g.f.: ((x+x^2/2+2*x^3/3)*exp(-x-x^2/2-x^3/3-x^4/4)+(1+x^2/2)*exp(-x-x^2/2-x^4/4))/(1-x)
%e A213323 Example: For n=5 the only permutations that fix no four-element subset are the 24 5-cycles and the 20 products of a 3-cycle and a 2-cycle, therefore a(5)=44.
%o A213323 (PARI)
%o A213323 x='x+O('x^66);
%o A213323 egf=((x+x^2/2+2*x^3/3)*exp(-x-x^2/2-x^3/3-x^4/4)+(1+x^2/2)*exp(-x-x^2/2-x^4/4))/(1-x);
%o A213323 Vec(serlaplace(egf))
%o A213323 /* _Joerg Arndt_, Jun 09 2012 */
%Y A213323 Cf. A000166, A137482, A213322, A213324
%K A213323 nonn
%O A213323 0,3
%A A213323 _Les Reid_, Jun 08 2012