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A096889 Initial values for f(x)=phi(sigma(x)) such that iteration of f ends in cycle of length=15. 11
467856, 480200, 490000, 499968, 514416, 523344, 524352, 531441, 548400, 549444, 550512, 553728, 556752, 560532, 562500, 562800, 570000, 570276, 570576, 573744, 576240, 579024, 579900, 581700, 584112, 584836, 586756, 590268, 595008, 599076 (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

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[599800], f[ # ] == 15 &]

PROG

(PARI) f(x, k=1)=for(i=1, k, x=eulerphi(sigma(x))); 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, 2)) && t!=(h=f(h, 2)) && t==f(h, 10) \\ Charles R Greathouse IV, Nov 25 2013

CROSSREFS

Cf. A000010, A000203, A095952, A096887, A095953, A096526, A095954, A096888, A096890, A095955, A095956.

Sequence in context: A213461 A051594 A238045 * A206205 A227767 A328255

Adjacent sequences:  A096886 A096887 A096888 * A096890 A096891 A096892

KEYWORD

nonn

AUTHOR

Labos Elemer and Robert G. Wilson v, Jul 14 2004

STATUS

approved

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Last modified October 19 21:28 EDT 2019. Contains 328244 sequences. (Running on oeis4.)