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

1,2

Links

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

Example

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

Mathematica

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

Prog

(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

Crossrefs

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

Sequence in context: A020204 A280389 A057489 * A211375 A326387 A217078

Adjacent sequences: A070808 A070809 A070810 * A070812 A070813 A070814

Keyword

nonn

Author

Labos Elemer, May 08 2002

Status

approved