A067129 Numbers k such that sigma(k-3) + sigma(k+3) = sigma(2*k).

5, 63, 99, 279, 355, 551, 561, 639, 1359, 1915, 2151, 2799, 4311, 8199, 8919, 10915, 12591, 13239, 16265, 16911, 17991, 18999, 20799, 24039, 24471, 28071, 28719, 30519, 33039, 35271, 40671, 43479, 45351, 48879, 51623, 52911, 56799, 60471, 63351, 74079, 75879

Offset

1,1

Comments

Conjecture: sequence gives odd values only.

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1..1000 from Donovan Johnson)

Mathematica

s[n_] := s[n] = DivisorSigma[1, n]; Select[Range[4, 80000], s[#-3] + s[#+3] == s[2*#] &] (* Amiram Eldar, May 03 2025 *)

Prog

(PARI) isok(n) = sigma(n-3)+sigma(n+3) == sigma(2*n); \\ Michel Marcus, Nov 20 2013

Crossrefs

Cf. A000203, A067172, A067730.

Sequence in context: A319624 A182118 A111387 * A209117 A238087 A063079

Adjacent sequences: A067126 A067127 A067128 * A067130 A067131 A067132

Keyword

nonn

Author

Benoit Cloitre, Feb 18 2002

Extensions

More terms from Michel Marcus, Nov 20 2013

Status

approved