A070807 - OEIS

A070807

Composite numbers n such that Cototient(totient(n))=A070556(n) is power of 2.

4, 6, 8, 9, 10, 12, 14, 15, 16, 18, 20, 21, 24, 26, 28, 30, 32, 34, 35, 36, 39, 40, 42, 45, 48, 51, 52, 56, 58, 60, 64, 65, 68, 70, 72, 78, 80, 84, 85, 87, 90, 96, 102, 104, 105, 112, 116, 119, 120, 128, 130, 136, 140, 144, 145, 153, 156, 160, 168, 170, 174, 180, 192

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OFFSET

1,1

LINKS

Table of n, a(n) for n=1..63.

EXAMPLE

n=87=3.29:phi[87]=56,56-phi[56]=56-24=32

MATHEMATICA

Do[s= EulerPhi[n]-EulerPhi[EulerPhi[n]]; If[IntegerQ[Log[2, s]]&&!PrimeQ[n], Print[n]], {n, 1, 10000000}]

CROSSREFS

Cf. A070556, A051953, A054571, A070806, A070809-A070811.

Sequence in context: A210441 A343597 A199009 * A246282 A374954 A046352

Adjacent sequences: A070804 A070805 A070806 * A070808 A070809 A070810

KEYWORD

nonn

AUTHOR

Labos Elemer, May 08 2002

STATUS

approved