A096889 Initial values for f(x)=phi(sigma(x)) such that iteration of f ends in cycle of length=15.

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

Offset: 1

Author

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

Keywords

• nonn

Links

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

Crossrefs

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

Programs

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 &]

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