A095954 Initial values for f(x)=phi(sigma(x)) such that iteration of f ends in a cycle of length 6.

784, 800, 882, 912, 960, 972, 1008, 1024, 1050, 1072, 1080, 1089, 1104, 1168, 1204, 1216, 1225, 1232, 1248, 1250, 1264, 1281, 1290, 1296, 1302, 1308, 1332, 1350, 1352, 1360, 1368, 1371, 1372, 1392, 1400, 1407, 1416, 1425, 1440, 1456, 1461, 1464, 1467

Offset: 1

Author

Labos Elemer, Jul 13 2004

Keywords

• nonn

Examples

			n=882:trajectory={882, 1296, 3300, [2880, 3024, 3840, 3456, 2560, 1800], 2880, ..}
		

Links

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

Crossrefs

Cf. A000010, A000203, A095952, A096887, A095953, A096526, A096888, A096889, 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[1500], f[ # ] == 6 &] (* Robert G. Wilson v, Jul 14 2004 *)

PARI

f(x)=eulerphi(sigma(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)) && t!=(h=f(h)) && t==f(f(f(h))) \\ Charles R Greathouse IV, Nov 23 2013