A067709 - OEIS

A067709

Numbers k such that phi(2*sigma(k)) = 2*sigma(phi(k)).

2, 4, 16, 18, 64, 100, 450, 516, 1458, 4096, 4624, 13932, 14406, 20124, 21780, 28900, 29262, 29616, 36450, 45996, 62500, 65536, 92778, 95916, 106092, 106308, 114630, 114930, 121872, 125652, 130050, 140130, 145794, 149124, 160986, 179562, 185100

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OFFSET

1,1

COMMENTS

Every even superperfect number (A019279) is a term of the sequence. - Vladeta Jovovic, Feb 11 2002

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..1000

MAPLE

with(numtheory); A067709:=n->`if`( phi(2*sigma(n)) = 2*sigma(phi(n)), n, NULL); seq(A067709(n), n=1..200000); # Wesley Ivan Hurt, Apr 07 2014

MATHEMATICA

Select[Range[200000], EulerPhi[2*DivisorSigma[1, #]] == 2*DivisorSigma[1, EulerPhi[#]] &] (* Amiram Eldar, May 13 2022 *)

PROG

(PARI) isok(k) = eulerphi(2*sigma(k)) == 2*sigma(eulerphi(k)); \\ Michel Marcus, May 13 2022

CROSSREFS

Cf. A000010, A000203, A019279.

Sequence in context: A217863 A186108 A131560 * A229238 A212202 A102545

Adjacent sequences: A067706 A067707 A067708 * A067710 A067711 A067712

KEYWORD

nonn

AUTHOR

Benoit Cloitre, Feb 05 2002

EXTENSIONS

More terms from Vladeta Jovovic, Feb 11 2002

STATUS

approved