A171259 - OEIS

%I #19 Jul 29 2024 19:01:07

%S 420,2730,5940,12540,24024,38610,48360,66528,77490,81510,133920,

%T 140448,141372,156420,163590,282720,284580,298452,348348,498420,

%U 600780,681912,701220,771420,792480,901530,918918,1016730,1052220,1150968,1372680,1439592,1654620

%N Numbers n such that sigma(n) = 14*phi(n) (where sigma=A000203, phi=A000010).

%H Amiram Eldar, <a href="/A171259/b171259.txt">Table of n, a(n) for n = 1..10000</a> (calculated using data from Jud McCranie, terms 1..1000 from Donovan Johnson)

%H Kevin A. Broughan and Daniel Delbourgo, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL16/Broughan/broughan26.html">On the Ratio of the Sum of Divisors and Euler’s Totient Function I</a>, Journal of Integer Sequences, Vol. 16 (2013), Article 13.8.8.

%H Kevin A. Broughan and Qizhi Zhou, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL17/Broughan/bro32.html">On the Ratio of the Sum of Divisors and Euler's Totient Function II</a>, Journal of Integer Sequences, Vol. 17 (2014), Article 14.9.2.

%t Select[Range[10^6], DivisorSigma[1, #] == 14 * EulerPhi[#] &] (* _Amiram Eldar_, Dec 04 2019 *)

%o (PARI) for(k=1,2e6, sigma(k) - 14*eulerphi(k) || print1(k", "));

%Y Cf. A062699, A068391, A068390, A136547, A104900, A136540, A104901, A163667, A171256, A171257, A104902, A171258, A171260, A104903.

%K nonn

%O 1,1

%A _Farideh Firoozbakht_ and _M. F. Hasler_, Mar 19 2010