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 A096526 Initial values for f(x)=phi(sigma(x)) such that iteration of f ends in a cycle of length 4. 10
 324, 400, 484, 490, 530, 544, 576, 630, 660, 672, 684, 690, 714, 722, 750, 756, 768, 770, 772, 777, 780, 792, 804, 810, 819, 828, 832, 833, 840, 841, 846, 852, 858, 864, 868, 870, 872, 876, 888, 892, 901, 906, 910, 918, 920, 924, 930, 936, 940, 948, 952 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Charles R Greathouse IV, Table of n, a(n) for n = 1..10000 EXAMPLE n=324: trajectory=324, 660, [576, 1512, 1280, 864], 576, ...} MATHEMATICA g[n_] := EulerPhi[ DivisorSigma[1, n]]; f[n_] := f[n] = Block[{lst = NestWhileList[g, n, UnsameQ, All ]}, -Subtract @@ Flatten[ Position[lst, lst[[ -1]]]]]; Select[ Range[1000], f[ # ] == 4 &] (* Robert G. Wilson v, Jul 14 2004 *) PROG (PARI) f(x)=eulerphi(sigma(x)) is(n)=my(t=f(n), h=f(t)); while(t!=h, t=f(t); h=f(f(h))); h=f(h); t!=h && t!=(h=f(h)) && t==f(f(h)) \\ Charles R Greathouse IV, Nov 22 2013 CROSSREFS Cf. A000010, A000203, A095952, A096887, A095953, A095954, A096888, A096889, A096890, A095955, A095956. Sequence in context: A088214 A117550 A045287 * A111278 A241502 A014792 Adjacent sequences: A096523 A096524 A096525 * A096527 A096528 A096529 KEYWORD nonn AUTHOR Labos Elemer, Jul 13 2004 STATUS approved

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Last modified May 29 12:08 EDT 2024. Contains 372940 sequences. (Running on oeis4.)