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 A124075 #20 Jul 13 2025 11:07:26
%S A124075 2,8,2417851639229258349412352
%N A124075 a(n) = 2^(3^(4^...^n)...).
%C A124075 The next term is too large to include.
%C A124075 The next term, a(5) = 2^(3^(4^5)), has 1.124...*10^488 digits. - _Amiram Eldar_, Jul 13 2025
%D A124075 David Applegate, Marc LeBrun and N. J. A. Sloane, Descending Dungeons and Iterated Base-Changing, in "The Mathematics of Preference, Choice and Order: Essays in Honor of Peter Fishburn", edited by Steven Brams, William V. Gehrlein and Fred S. Roberts, Springer, 2009, pp. 393-402.
%H A124075 David Applegate, Marc LeBrun and N. J. A. Sloane, <a href="https://arxiv.org/abs/math/0611293">Descending Dungeons and Iterated Base-Changing</a>, arXiv:math/0611293 [math.NT], 2006-2007.
%H A124075 David Applegate, Marc LeBrun, N. J. A. Sloane, <a href="https://www.jstor.org/stable/40391135">Descending Dungeons, Problem 11286</a>, Amer. Math. Monthly, 116 (2009) 466-467.
%e A124075 a(4) = 2^(3^4) = 2417851639229258349412352.
%t A124075 a[n_] := Fold[#2^#1&, n, Range[2, n-1] // Reverse];
%t A124075 Table[a[n], {n, 2, 4}] (* _Jean-François Alcover_, Oct 10 2018 *)
%Y A124075 Cf. A014221, A049384, A121263, A121265, A121295, A121296.
%K A124075 nonn,bref
%O A124075 2,1
%A A124075 _David Applegate_ and _N. J. A. Sloane_, Nov 08 2006