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 A122215 #54 Aug 25 2023 09:42:47
%S A122215 1,1,3,27,3645,61509375,4204742431640625,
%T A122215 2396825584582984447479248046875,
%U A122215 3896237517467890187050354408614984136338676989907980896532535552978515625
%N A122215 Denominators in infinite products for Pi/2, e and e^gamma (reduced).
%H A122215 Seiichi Manyama, <a href="/A122215/b122215.txt">Table of n, a(n) for n = 1..12</a>
%H A122215 Mohammad K. Azarian, <a href="http://www.m-hikari.com/ijcms/ijcms-2012/21-24-2012/azarianIJCMS21-24-2012.pdf">Euler's Number Via Difference Equations</a>, International Journal of Contemporary Mathematical Sciences, Vol. 7, 2012, No. 22, pp. 1095 - 1102.
%H A122215 J. Baez, <a href="http://math.ucr.edu/home/baez/week230.html">This Week's Finds in Mathematical Physics</a>
%H A122215 J. Guillera and Jonathan Sondow, <a href="http://arXiv.org/abs/math.NT/0506319">Double integrals and infinite products for some classical constants via analytic continuations of Lerch's transcendent</a>, Ramanujan J. 16 (2008) 247-270.
%H A122215 Jonathan Sondow, <a href="https://arxiv.org/abs/math/0401406">A faster product for Pi and a new integral for ln Pi/2</a>, arXiv:math/0401406 [math.NT], 2004.
%H A122215 Jonathan Sondow, <a href="https://www.jstor.org/stable/30037575">A faster product for Pi and a new integral for ln Pi/2</a>, Amer. Math. Monthly 112 (2005) 729-734.
%F A122215 a(n) = denominator(Product_{k=1..n} k^((-1)^k*binomial(n-1,k-1))).
%F A122215 For n>=2, a(n) = denominator(exp(-2 * Integral_{x=0..1} x^(2*n-1)/log(1-x^2) dx)) (see Mathematica code below). - _John M. Campbell_, Jul 18 2011
%F A122215 For n>=2, a(n) = denominator(exp((1/n)*Integral_{x=0..oo} (1-exp(-1/x))^n dx)). - _Federico Provvedi_, Jun 29 2023
%e A122215 Pi/2 = (2/1)^(1/2) * (4/3)^(1/4) * (32/27)^(1/8) * (4096/3645)^(1/16) * ...,
%e A122215 e = (2/1)^(1/1) * (4/3)^(1/2) * (32/27)^(1/3) * (4096/3645)^(1/4) * ... and
%e A122215 e^gamma = (2/1)^(1/2) * (4/3)^(1/3) * (32/27)^(1/4) * (4096/3645)^(1/5) *
%e A122215 ...
%t A122215 Table[Exp[-2*Integrate[x^(2n-1)/Log[1-x^2],{x,0,1}]],{n,2,8}]
%t A122215 Denominator@Table[Product[k^((-1)^k Binomial[n-1, k-1]), {k, 1, n}], {n, 1, 10}] (* _Vladimir Reshetnikov_, May 29 2016 *)
%o A122215 (PARI) {a(n) = denominator(prod(k=1, n, k^((-1)^k*binomial(n-1,k-1))))} \\ _Seiichi Manyama_, Mar 10 2019
%Y A122215 Cf. A092799. Numerators are A122214. Unreduced denominators are A122217.
%K A122215 frac,nonn
%O A122215 1,3
%A A122215 _Jonathan Sondow_, Aug 26 2006