A137733 Numbers n such that sigma(2*phi(n)) = 2*sigma(n).

2318, 2806, 5734, 5937, 7198, 8097, 10126, 11295, 11818, 13054, 17324, 20374, 21838, 22947, 27694, 29145, 32086, 33826, 35074, 38997, 42334, 42458, 43798, 46726, 54825, 56974, 58438, 61366, 66202, 68686, 71614, 86762, 86924, 87435

Offset

1,1

Links

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Jean-Marie De Koninck and Florian Luca, Positive integers n such that sigma(phi(n)) = sigma(n), Journal of Integer Sequences, Paper No. 08.1.5, 2008.

Example

a(1) = 2318, because this is the smallest integer such that sigma(2*phi(n)) = 2*sigma(n).

Mathematica

Select[Range[90000], DivisorSigma[1, 2*EulerPhi[#]]==2*DivisorSigma[1, #]&] (* Harvey P. Dale, Jan 31 2015 *)

Prog

(PARI) is(n)=sigma(2*eulerphi(n))==2*sigma(n) \\ Charles R Greathouse IV, Feb 04 2013

Crossrefs

Sequence in context: A133538 A075668 A210175 * A205636 A347569 A250998

Adjacent sequences: A137730 A137731 A137732 * A137734 A137735 A137736

Keyword

nonn

Author

Jeffrey Shallit, Feb 09 2008; definition corrected Feb 09 2008

Status

approved