A096888 - OEIS

%I #8 Nov 25 2013 11:11:04

%S 76050,88452,88896,95922,104364,104988,106032,108252,110450,110928,

%T 112896,113052,113412,113868,115572,119892,119916,121680,122220,

%U 122832,122916,123060,123312,129600,129840,129984,130260,130560,131280,133860

%N Initial values for f(x)=phi(sigma(x)) such that iteration of f ends in cycle of length=11.

%H Charles R Greathouse IV, <a href="/A096888/b096888.txt">Table of n, a(n) for n = 1..10000</a>

%t 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[134000], f[ # ] == 11 &]

%o (PARI) f(x,k=1)=for(i=1,k,x=eulerphi(sigma(x))); x

%o 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==f(h,10) \\ _Charles R Greathouse IV_, Nov 25 2013

%Y Cf. A000010, A000203, A095952, A096887, A095953, A096526, A095954, A096889, A096890, A095955, A095956.

%K nonn

%O 1,1

%A _Labos Elemer_ and _Robert G. Wilson v_, Jul 14 2004