A171258 Numbers n such that sigma(n) = 13*phi(n) (where sigma=A000203, phi=A000010).

630, 5544, 11160, 18810, 27000, 57000, 80388, 161820, 178020, 182880, 242820, 265608, 388620, 391500, 447678, 465192, 522522, 671760, 690120, 711000, 775170, 826500, 901170, 1051830, 1102290, 1157130, 1418160, 1578330, 1679400, 1812384, 1874520, 1993824

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[2*10^6], DivisorSigma[1, #]==13EulerPhi[#]&] (* Harvey P. Dale, Mar 29 2018 *)

Prog

(PARI) for(k=1, 2e6, sigma(k) - 13*eulerphi(k) || print1(k", "));

Crossrefs

Cf. A062699, A068391, A068390, A136547, A104900, A136540, A104901, A163667, A171256, A171257, A104902, A171259, A171260, A104903.

Sequence in context: A173423 A295769 A110904 * A234245 A234241 A185849

Adjacent sequences: A171255 A171256 A171257 * A171259 A171260 A171261

Keyword

nonn

Author

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

Status

approved