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 A004733 #17 Oct 26 2023 01:04:24 %S A004733 3,8,15,16,105,128,315,256,3465,1024,9009,2048,45045,32768,109395, %T A004733 65536,2078505,262144,4849845,524288,22309287,4194304,50702925, %U A004733 8388608,456326325,33554432,1017958725,67108864 %N A004733 Denominator of n!!/(n+3)!!. %D A004733 S. Janson, On the traveling fly problem, Graph Theory Notes of New York, Vol. XXXI, 17, 1996. %H A004733 S. Janson, <a href="http://www2.math.uu.se/~svante/papers/sj114.pdf">On the traveling fly problem</a>. %o A004733 (PARI) a(n) = denominator(prod(i=0, floor((n-1)/2), n-2*i)/prod(i=0, floor((n+2)/2), n+3-2*i)) \\ _Michel Marcus_, May 24 2013 %Y A004733 Cf. A004732. %Y A004733 Cf. A001801. %K A004733 nonn,frac %O A004733 0,1 %A A004733 _N. J. A. Sloane_