A070810 Nonprime numbers k such that phi(k-phi(k)) = A054571(k) is a power of 2.

4, 6, 8, 9, 10, 12, 14, 16, 18, 20, 22, 24, 25, 28, 32, 36, 38, 39, 40, 42, 44, 46, 48, 50, 55, 56, 58, 62, 64, 65, 72, 76, 77, 80, 84, 88, 92, 94, 96, 100, 112, 116, 118, 124, 128, 134, 144, 152, 158, 160, 165, 168, 176, 184, 188, 192, 200, 202, 224, 232, 235, 236

Offset

1,1

Links

Amiram Eldar, Table of n, a(n) for n = 1..6018 (terms below 10^10)

Example

For k = 168: 168 - phi(168) = 168-48 = 120, phi(120) = 32, 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 || 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, A070811, A070812.

Sequence in context: A327776 A102554 A371862 * A391242 A227180 A129930

Adjacent sequences: A070807 A070808 A070809 * A070811 A070812 A070813

Keyword

nonn

Author

Labos Elemer, May 08 2002

Status

approved