A067130 Numbers k such that sigma(k-1) divides sigma(k+1).

2, 34, 55, 119, 285, 367, 835, 849, 919, 1241, 1505, 1559, 2911, 2914, 2939, 3305, 4149, 4188, 6111, 6903, 7170, 7913, 9360, 10251, 10541, 12566, 15086, 17273, 17759, 17815, 19005, 19689, 19919, 21411, 21462, 24882, 25020, 26610, 28125, 30593, 30789, 31485

Offset

1,1

Links

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

Mathematica

Flatten[Position[Partition[DivisorSigma[1, Range[32000]], 3, 1], _?( Divisible[ Last[#], First[#]]&), {1}, Heads->False]]+1 (* Harvey P. Dale, Jan 13 2015 *)

Prog

(PARI) isok(n) = sigma(n+1) % sigma(n-1) == 0; \\ Michel Marcus, Nov 20 2013

Crossrefs

Cf. A000203 (sigma), A055574.

Sequence in context: A124208 A077310 A177051 * A349496 A337397 A263226

Adjacent sequences: A067127 A067128 A067129 * A067131 A067132 A067133

Keyword

nonn

Author

Benoit Cloitre, Feb 18 2002

Extensions

More terms from Michel Marcus, Nov 20 2013

Status

approved