A015913 Numbers k such that sigma(k) + 4 = sigma(k+4).

3, 7, 13, 19, 37, 43, 67, 79, 97, 103, 109, 127, 163, 193, 223, 229, 277, 307, 313, 349, 379, 397, 439, 457, 463, 487, 499, 613, 643, 673, 739, 757, 769, 823, 853, 859, 877, 883, 907, 937, 967, 1009, 1087, 1093, 1213, 1279, 1297, 1303, 1423

Offset: 1

Author

Robert G. Wilson v

Keywords

• nonn

Comments

This sequence contains the composite number 305635357, so is different from A023200 and A029710 (305635357 is the only composite member of the present sequence below 10^9). - Jud McCranie, Jan 07 2001

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A023200, A029710.

Programs

Mathematica

Select[Range[1500],DivisorSigma[1,#]+4==DivisorSigma[1,#+4]&] (* Harvey P. Dale, Nov 04 2011 *)

PARI

is(n)=sigma(n)+4==sigma(n+4) \\ Charles R Greathouse IV, Mar 09 2014