A065556 Numbers n such that sigma (phi ( n ) ) = sigma (sigma (n ) ) where phi is Euler's totient and sigma is the multiplicative sum-of-divisors function.

1, 367, 919, 1967, 3641, 4379, 5143, 7379, 11843, 12767, 13493, 15293, 21797, 26039, 28381, 29807, 30263, 30593, 30599, 30887, 37523, 40199, 48559, 49781, 51101, 51397, 55277, 62573, 67223, 72433, 73979, 87047, 89255, 89851, 95393

Offset

1,2

Links

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

Formula

sigma(phi(n)) = sigma(sigma(n)).

Example

367 is in the sequence because phi(367) = 366, sigma(367) = 368, sigma(366) = 744 = sigma(368).

Mathematica

Select[Range[100000], DivisorSigma[1, EulerPhi[#]]==DivisorSigma[ 1, DivisorSigma[1, #]]&] (* Harvey P. Dale, Jun 23 2013 *)

Prog

(PARI) { n=0; for (m=1, 10^9, if (sigma(eulerphi(m)) == sigma(sigma(m)), write("b065556.txt", n++, " ", m); if (n==1000, return)) ) } \\ Harry J. Smith, Oct 22 2009

Crossrefs

Cf. A033632, A000010, A000203.

Sequence in context: A059230 A212378 A060518 * A068357 A067891 A142579

Adjacent sequences: A065553 A065554 A065555 * A065557 A065558 A065559

Keyword

nonn

Author

Walter Nissen, Nov 28 2001

Status

approved