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A095952 Initial values for f(x)=phi(sigma(x)) such that iteration of f ends in cycle of length=1. 14
1, 2, 3, 5, 8, 9, 12, 14, 15, 19, 20, 22, 23, 26, 29, 41, 43, 128, 156, 168, 186, 189, 200, 201, 217, 231, 237, 240, 248, 254, 260, 266, 271, 285, 291, 297, 303, 304, 313, 314, 329, 332, 335, 337, 341, 346, 350, 366, 368, 383, 387, 395, 413, 427, 430, 436, 437 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

EXAMPLE

n=100: trajectory={980, 648, 880, 720, 720}

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[1540], f[ # ] == 1 &] (* Robert G. Wilson v, Jul 14 2004 *)

PROG

(PARI) is(n)=my(t=f(n), h=f(t)); while(t!=h, t=f(t); h=f(f(h))); t==f(t) \\ Charles R Greathouse IV, Nov 22 2013

CROSSREFS

Cf. A000010, A000203, A096887, A095953, A096526, A095954, A096888, A096889, A096890, A095955, A095956.

Sequence in context: A181155 A153081 A190841 * A286492 A025033 A122933

Adjacent sequences:  A095949 A095950 A095951 * A095953 A095954 A095955

KEYWORD

nonn

AUTHOR

Labos Elemer, Jul 13 2004

STATUS

approved

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Last modified November 13 02:59 EST 2019. Contains 329085 sequences. (Running on oeis4.)