A096998 - OEIS

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A096998

Consider iteration of the function f(x) = sigma(phi(x)) = A062402(x). Sequence lists the numbers k such that the trajectory of k returns to k.

1, 3, 7, 12, 15, 28, 31, 60, 72, 124, 168, 195, 252, 255, 744, 1240, 1512, 1651, 2418, 2520, 3066, 3844, 4092, 4800, 5080, 5376, 6045, 6138, 6552, 9906, 9920, 10200, 12264, 20440, 30855, 36792, 46228, 58968, 60984, 65535, 67963, 81880, 122640

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OFFSET

1,2

LINKS

Table of n, a(n) for n=1..43.

EXAMPLE

96 => 63 => 91 => 195 => 252 => 195 => ..., therefore 195 and 252 are in the sequence.

MATHEMATICA

a = {}; f[n_] := DivisorSigma[1, EulerPhi[ n]]; Do[ AppendTo[ a, NestWhileList[f, n, UnsameQ, All][[ -1]]]; a = Union[a], {n, 10^6}]; Take[ a, 43] (* Robert G. Wilson v, Jul 21 2004 *)

CROSSREFS

Cf. A062402, A096850.

Sequence in context: A225574 A317305 A356425 * A356353 A317307 A331042

Adjacent sequences: A096995 A096996 A096997 * A096999 A097000 A097001

KEYWORD

nonn

AUTHOR

Labos Elemer, Jul 19 2004

EXTENSIONS

Edited, corrected and extended by Robert G. Wilson v, Jul 21 2004

STATUS

approved