A070811 Nonprime numbers k such that phi(k-phi(k)) = A054571(k) is not a power of 2.

1, 15, 21, 26, 27, 30, 33, 34, 35, 45, 49, 51, 52, 54, 57, 60, 63, 66, 68, 69, 70, 74, 75, 78, 81, 82, 85, 86, 87, 90, 91, 93, 95, 98, 99, 102, 104, 105, 106, 108, 110, 111, 114, 115, 117, 119, 120, 121, 122, 123, 125, 126, 129, 130, 132, 133, 135, 136, 138, 140

Offset: 1

Author

Labos Elemer, May 08 2002

Keywords

• nonn

Examples

			For k = 30: phi(30) = 8, cototient(30) = 22, phi(22) = 10 is not a power of 2.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000010, A054571, A051953, A070556, A070806, A070807, A070809, A070810, A070812.

Programs

Mathematica

Do[s=EulerPhi[n-EulerPhi[n]]; If[ !IntegerQ[Log[2, s]]&&!PrimeQ[n], Print[n]], {n, 1, 256}]

PARI

is(k) = if(k == 1, 1, if(isprime(k), 0, my(m = eulerphi(k - eulerphi(k))); m >> valuation(m, 2) > 1)); \\ Amiram Eldar, Nov 08 2024