A084821 - OEIS

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A084821

Odd numbers m such that sigma(m) > m + phi(m), where sigma=A000203 is the divisor sum and phi=A000010 the totient.

15, 45, 63, 75, 105, 135, 165, 189, 195, 225, 231, 255, 273, 285, 297, 315, 345, 357, 375, 399, 405, 429, 435, 441, 465, 483, 495, 525, 555, 567, 585, 609, 615, 645, 651, 675, 693, 705, 735, 765, 777, 795, 819, 825, 855, 861, 885, 891, 903, 915, 945, 975

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OFFSET

1,1

COMMENTS

This sequence is closed under multiplication by odd values, and in particular with multiplication by itself. - Charles R Greathouse IV, Feb 19 2013

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000

MATHEMATICA

Select[Range[1, 1000, 2], DivisorSigma[1, #] > EulerPhi[#] + # &] (* Amiram Eldar, Sep 12 2019 *)

PROG

(PARI) is(n)=n%2 && sigma(n)>eulerphi(n)+n \\ Charles R Greathouse IV, Feb 19 2013

CROSSREFS