A065555 Numbers n such that phi(phi(n)) = phi(sigma(n)) where phi is Euler's totient and sigma is the multiplicative sum-of-divisors function.

1, 5, 11, 71, 145, 319, 323, 377, 779, 865, 911, 1007, 1073, 1167, 1195, 1343, 1441, 1585, 1609, 1691, 1903, 2117, 2147, 2249, 2591, 2629, 2723, 2987, 3013, 3107, 3239, 3247, 3265, 3383, 3487, 3569, 3777, 3791, 3827, 4121, 4199, 4339, 5249, 5455, 5597

Offset

1,2

Links

Harry J. Smith, Table of n, a(n) for n=1,...,1000

Example

5 is in the sequence because phi(5) = 4, sigma(5) = 6, phi(4) = 2 = phi(6).

Prog

(PARI) { n=0; for (m=1, 10^9, if (eulerphi(eulerphi(m)) == eulerphi(sigma(m)), write("b065555.txt", n++, " ", m); if (n==1000, return)) ) } \\ Harry J. Smith, Oct 22 2009

Crossrefs

Cf. A033632, A000010, A000203.

Sequence in context: A101209 A216071 A050568 * A189802 A328453 A175207

Adjacent sequences: A065552 A065553 A065554 * A065556 A065557 A065558

Keyword

nonn

Author

Walter Nissen, Nov 28 2001

Status

approved