A015867 Numbers k such that sigma(k) = sigma(k+7).

10, 62, 188, 362, 759, 1178, 1214, 1431, 1442, 1598, 1695, 1748, 2235, 3495, 6699, 9338, 9945, 11438, 13695, 18795, 20727, 26199, 26631, 30548, 35438, 53751, 79826, 79827, 89378, 103887, 114231, 122738, 132111, 135506, 138135

Offset: 1

Author

Robert G. Wilson v

Keywords

• nonn

References

• J.-M. De Koninck, Ces nombres qui nous fascinent, Entry 62, p. 22, Ellipses, Paris 2008.

Links

• Donovan Johnson, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A002961, A007373, A015861, A015863, A015865, A015866, A015876, A015877, A015880, A015881, A015882, A015883, A181647.

Programs

Mathematica

Select[Range[140000], DivisorSigma[1, #]==DivisorSigma[1, # + 7] &] (* Vincenzo Librandi, Mar 10 2014 *)

PARI

is(n)=sigma(n)==sigma(n+7) \\ Charles R Greathouse IV, Mar 09 2014