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 A049100 a(n) = Euler phi function applied 4 times to n. 6
 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, 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, 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,17 LINKS Antti Karttunen, Table of n, a(n) for n = 1..10000 Boris Putievskiy, Transformations [Of] Integer Sequences And Pairing Functions, arXiv preprint arXiv:1212.2732, 2012. FORMULA a(n) = phi(phi(phi(phi(n)))) = A000010(A000010(A000010(A000010(n)))) = A010554(A010554(n)) = A000010(A049099(n)). EXAMPLE 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. MAPLE with(numtheory): seq(phi(phi(phi(phi(n)))), n=1..130); # Emeric Deutsch, May 14 2006 MATHEMATICA a(n)=Nest[ EulerPhi, n, 4 ] PROG (PARI) A049100(n) = eulerphi(eulerphi(eulerphi(eulerphi(n)))); \\ Antti Karttunen, Aug 22 2017 CROSSREFS Cf. A000010, A010554, A049099, A049107, A049115. Sequence in context: A071625 A309004 A304779 * A276088 A030612 A327528 Adjacent sequences:  A049097 A049098 A049099 * A049101 A049102 A049103 KEYWORD nonn AUTHOR EXTENSIONS Edited by N. J. A. Sloane at the suggestion of Andrew S. Plewe, Jun 23 2007 STATUS approved

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Last modified January 25 07:33 EST 2020. Contains 331241 sequences. (Running on oeis4.)