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%I #16 May 08 2021 07:40:22
%S 1,4,8,24,120,1170,1512,15748,15748,61440,196584,1572840,1098240,
%T 15605760,50328576,7074432,355532800,2143289344,13815410400,
%U 224319234048,33541980160,109760857440,1468475386560,33151875434496,1415960985600,1510712608204800
%N a(n) = sigma^n(n), where sigma^n denotes functional iteration.
%C 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 a(88) = a(89), a(108) = a(109) and a(124) = a(125). - _Seiichi Manyama_, May 08 2021
%H Seiichi Manyama, <a href="/A090896/b090896.txt">Table of n, a(n) for n = 1..200</a>
%e a(3) = sigma^3(3) = sigma^2(4) = sigma(7) = 8
%p a:= n-> (numtheory[sigma]@@n)(n):
%p seq(a(n), n=1..30); # _Alois P. Heinz_, Oct 03 2018
%o (PARI) a(n) = my(k=sigma(n)); for(n=2, n, k=sigma(k)); k; \\ _Seiichi Manyama_, May 08 2021
%Y Main diagonal of A129246.
%Y Cf. A000203, A101303.
%K nonn
%O 1,2
%A Gabriel Cunningham (gcasey(AT)mit.edu), Feb 25 2004
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