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A171257 Numbers n such that sigma(n) = 11*phi(n) (where sigma=A000203, phi=A000010). 5
2580, 16770, 18630, 28896, 35970, 61404, 66024, 147576, 163944, 215124, 224010, 296184, 399126, 408672, 443394, 464340, 476010, 574308, 856086, 862752, 868428, 931224, 957348, 1004910, 1110186, 1496610, 1721720, 1723290, 1833348, 1971288, 2139852, 2234790 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000 (calculated using data from Jud McCranie, terms 1..1000 from Donovan Johnson)

Kevin A. Broughan and Daniel Delbourgo, On the Ratio of the Sum of Divisors and Euler’s Totient Function I, Journal of Integer Sequences, Vol. 16 (2013), Article 13.8.8.

Kevin A. Broughan and Qizhi Zhou, On the Ratio of the Sum of Divisors and Euler's Totient Function II, Journal of Integer Sequences, Vol. 17 (2014), Article 14.9.2.

MATHEMATICA

Select[Range[10^6], DivisorSigma[1, #] == 11 * EulerPhi[#] &] (* Amiram Eldar, Dec 04 2019 *)

PROG

(PARI) for(k=1, 2e6, sigma(k) - 11*eulerphi(k) | print1(k", "));

CROSSREFS

Cf. A062699, A068391, A068390, A136547, A104900, A136540, A104901, A163667, A171256, A104902, A171258, A171259, A171260, A104903.

Sequence in context: A201510 A303400 A235094 * A252159 A252167 A252160

Adjacent sequences:  A171254 A171255 A171256 * A171258 A171259 A171260

KEYWORD

nonn

AUTHOR

Farideh Firoozbakht and M. F. Hasler, Mar 19 2010

STATUS

approved

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Last modified July 11 04:33 EDT 2020. Contains 335609 sequences. (Running on oeis4.)