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 A102263 #19 Dec 11 2021 02:11:23 %S A102263 1,4,36,144,1800,43200,705600,705600,2116800,127008000,23051952000, %T A102263 6638962176000,280496151936000,31415569016832000,471233535252480000, %U A102263 471233535252480000,54474596675186688000,3268475800511201280000 %N A102263 Denominators of probabilities in gift exchange problem with n people. %C A102263 n friends organize a gift exchange. The n names are put into a hat and the first person draws one. If she picks her own name, then she returns it to the bag and draws again, repeating until she has a name that is not her own. Then the second person draws, again returning his own name if it is drawn. This continues down the line. What is the probability p(n) that when the n-th person draws, only her own name will be left in the bag? %C A102263 I heard about the problem from Gary Thompson at Grove City College in PA. %H A102263 Jon E. Schoenfield, <a href="/A102263/b102263.txt">Table of n, a(n) for n = 2..389</a> %H A102263 Math Forum at Drexel, <a href="http://mathforum.org/kb/message.jspa?messageID=6667330&tstart=0">A variant on the "Secret Santa"</a> %F A102263 See A102262 for formula for p(n). %e A102263 p(2) through p(10) are 0, 1/4, 5/36, 19/144, 203/1800, 4343/43200, 63853/705600, 58129/705600, 160127/2116800. %Y A102263 Cf. A102262, A136300. %K A102263 nonn,frac %O A102263 2,2 %A A102263 _Jerrold Grossman_, Feb 17 2005 %E A102263 More terms from _Jon E. Schoenfield_, Sep 30 2006