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 A090896 #20 Jan 30 2025 11:21:52
%S A090896 1,4,8,24,120,1170,1512,15748,15748,61440,196584,1572840,1098240,
%T A090896 15605760,50328576,7074432,355532800,2143289344,13815410400,
%U A090896 224319234048,33541980160,109760857440,1468475386560,33151875434496,1415960985600,1510712608204800
%N A090896 a(n) = sigma^n(n), where sigma^n denotes functional iteration.
%C A090896 a(8) = a(9). Are there any other numbers m, n such that a(m) = a(n)? a(16) < a(15); a(25) < a(24). How often is a(n+1) < a(n)?
%C A090896 a(88) = a(89), a(108) = a(109) and a(124) = a(125). - _Seiichi Manyama_, May 08 2021
%H A090896 Seiichi Manyama, <a href="/A090896/b090896.txt">Table of n, a(n) for n = 1..200</a>
%e A090896 a(3) = sigma^3(3) = sigma^2(4) = sigma(7) = 8
%p A090896 a:= n-> (numtheory[sigma]@@n)(n):
%p A090896 seq(a(n), n=1..30); # _Alois P. Heinz_, Oct 03 2018
%t A090896 a[n_] := Nest[DivisorSigma[1, #]&, n, n];
%t A090896 Table[a[n], {n, 1, 30}] (* _Jean-François Alcover_, Jan 30 2025 *)
%o A090896 (PARI) a(n) = my(k=sigma(n)); for(n=2, n, k=sigma(k)); k; \\ _Seiichi Manyama_, May 08 2021
%Y A090896 Main diagonal of A129246.
%Y A090896 Cf. A000203, A101303.
%K A090896 nonn
%O A090896 1,2
%A A090896 Gabriel Cunningham (gcasey(AT)mit.edu), Feb 25 2004