A015880 Numbers k such that sigma(k) = sigma(k+10).

21, 174, 270, 517, 572, 913, 992, 1002, 1420, 1633, 1830, 2622, 2958, 4170, 4747, 5539, 7520, 7544, 7729, 10184, 10783, 14863, 16165, 16520, 19837, 20935, 21584, 23161, 26840, 28544, 29737, 31453, 34510, 35571, 35611, 35845, 39560

Offset: 1

Author

Robert G. Wilson v

Keywords

• nonn

Links

• Donovan Johnson, Table of n, a(n) for n = 1..1000
• A. Weingartner, On the Solutions of sigma(n) = sigma(n+k), Journal of Integer Sequences, Vol. 14 (2011), #11.5.5.

Crossrefs

Cf. A002961, A007373, A015861, A015863, A015865, A015866, A015867, A015876, A015877, A015881, A015882, A015883, A181647.

Programs

Mathematica

Select[Range[40000], DivisorSigma[1, #]==DivisorSigma[1, # + 10] &] (* Vincenzo Librandi, Mar 10 2014 *)

PARI

is(n)=sigma(n)==sigma(n+10) \\ Charles R Greathouse IV, Mar 09 2014