A067224 Numbers k such that phi(5k-1) = sigma(k).

5225, 20405, 181685, 210395, 302375, 302445, 524975, 1469555, 1563485, 1748855, 2791085, 3097055, 4418375, 4542065, 4735115, 5482235, 5567705, 5568615, 5683205, 5753405, 6457055, 7363013, 7531205, 8016435, 8043875, 9534185, 10511345, 10790325, 11504405

Offset

1,1

Comments

Are there any terms not congruent to 5 in the sequence?

a(22) = 7363013 is the first example. - Charles R Greathouse IV, Jan 29 2012

Links

Table of n, a(n) for n=1..29.

Mathematica

Select[Range[10^6], EulerPhi[5*# - 1] == DivisorSigma[1, #] &] (* Amiram Eldar, May 09 2022 *)

Prog

(PARI) for(n=1, 1e8, if(sigma(n)==eulerphi(5*n-1), print1(n", "))) \\ Charles R Greathouse IV, Jan 29 2012

Crossrefs

Cf. A000010, A000203, A067226, A067235.

Sequence in context: A231113 A289514 A031616 * A204139 A237408 A235296

Adjacent sequences: A067221 A067222 A067223 * A067225 A067226 A067227

Keyword

nonn

Author

Benoit Cloitre, Feb 20 2002

Extensions

a(8)-a(29) from Donovan Johnson, Jan 29 2012

Status

approved