A065822 Numbers k such that 5*phi(k) = 4*sigma(k).

323, 377, 22591, 42619, 49751, 106711, 119647, 180947, 2782057, 2980823, 2981233, 3794737, 5112427, 5285743, 5732179, 5964229, 6073267, 6669797, 6769927, 7049407, 8025547, 8350633, 8954023, 9373213, 10039471, 10140517, 10842901

Offset: 1

Author

Labos Elemer, Nov 23 2001

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..335 (terms 1..60 from Harry J. Smith)

Crossrefs

Cf. A000010, A000203, A065818, A065819, A062699.

Programs

Mathematica

Select[Range[1085*10^4],5EulerPhi[#]==4DivisorSigma[1,#]&] (* Harvey P. Dale, Aug 11 2019 *)

PARI

{ n=0; for (m=1, 10^9, if (5*eulerphi(m) == 4*sigma(m), write("b065822.txt", n++, " ", m); if (n==60, return)) ) } \\ Harry J. Smith, Nov 01 2009

PARI

is(n) = {my(f=factor(n)); 5*eulerphi(f) == 4*sigma(f);} \\ Amiram Eldar, Jun 26 2024

Extensions

a(9)-a(27) from Harry J. Smith, Nov 01 2009