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A070807 Composite numbers n such that Cototient(totient(n))=A070556(n) is power of 2. 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 (list; graph; refs; listen; history; text; internal format)
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: A077094 A210441 A199009 * A246282 A046352 A046355

Adjacent sequences:  A070804 A070805 A070806 * A070808 A070809 A070810

KEYWORD

nonn

AUTHOR

Labos Elemer, May 08 2002

STATUS

approved

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Last modified February 16 14:47 EST 2019. Contains 320163 sequences. (Running on oeis4.)