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 A049100 #24 Nov 29 2023 06:58:10 %S A049100 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2,1,1,1,1,1,2,1,2,1,1,1,2,1,2,2,2,2, %T A049100 2,1,2,1,2,2,4,1,2,2,2,2,4,2,2,2,4,2,4,1,4,2,2,2,4,2,4,2,2,4,4,2,4,4, %U A049100 4,2,4,2,4,2,4,2,4,2,4,4,2,4,8,2,8,2,4,4,8,2,4,4,4,4,4,4,8,2,4,4,8,4,8,4,4 %N A049100 a(n) = Euler phi function applied 4 times to n. %H A049100 Antti Karttunen, <a href="/A049100/b049100.txt">Table of n, a(n) for n = 1..10000</a> %H A049100 Boris Putievskiy, <a href="http://arxiv.org/abs/1212.2732">Transformations [Of] Integer Sequences And Pairing Functions</a>, arXiv preprint arXiv:1212.2732 [math.CO], 2012. %F A049100 a(n) = phi(phi(phi(phi(n)))) = A000010(A000010(A000010(A000010(n)))) = A010554(A010554(n)) = A000010(A049099(n)). %e A049100 n=163, the successive iterates applying Euler totient function are as follows: 163,162,54,18,6,2,1. The 5th term is 6, when Phi was applied 4 times. So a(163)=6. %p A049100 with(numtheory): seq(phi(phi(phi(phi(n)))),n=1..130); # _Emeric Deutsch_, May 14 2006 %t A049100 a(n)=Nest[ EulerPhi, n, 4 ] %o A049100 (PARI) A049100(n) = eulerphi(eulerphi(eulerphi(eulerphi(n)))); \\ _Antti Karttunen_, Aug 22 2017 %Y A049100 Cf. A000010, A010554, A049099, A049107, A049115. %K A049100 nonn %O A049100 1,17 %A A049100 _Labos Elemer_ %E A049100 Edited by _N. J. A. Sloane_ at the suggestion of _Andrew S. Plewe_, Jun 23 2007