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A096889
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Initial values for f(x)=phi(sigma(x)) such that iteration of f ends in cycle of length=15.
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11
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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
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OFFSET
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1,1
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LINKS
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MATHEMATICA
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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 &]
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PROG
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(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
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CROSSREFS
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Cf. A000010, A000203, A095952, A096887, A095953, A096526, A095954, A096888, A096890, A095955, A095956.
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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