A227304 Numbers k such that sigma(k+1) divides sigma(k-1).

34, 55, 285, 367, 835, 849, 919, 1241, 1505, 2911, 2914, 3305, 4149, 4188, 6111, 6903, 7170, 7913, 8506, 9360, 10251, 10541, 12566, 15086, 17273, 17815, 19005, 19689, 21411, 21462, 24882, 25020, 25501, 26610, 28125, 30361, 30593, 30789, 31485, 37741, 38211, 38983, 39787

Offset

1,1

Comments

The sequence consists mainly of terms of A055574 = { n | sigma(n+1) = sigma(n-1) }. - M. F. Hasler, Aug 06 2015

Links

Amiram Eldar, Table of n, a(n) for n = 1..6000 (term 1..280 from Harvey P. Dale)

Example

Sigma(8507) = 8736 divides sigma(8505) = 17472 = 8736*2, so 8506 is in the sequence.

Mathematica

Flatten[Position[Partition[DivisorSigma[1, Range[40000]], 3, 1], _?(Divisible[ #[[1]], #[[3]]]&), {1}, Heads->False]]+1 (* Harvey P. Dale, Jul 15 2014 *)

Crossrefs

Cf. A000203, A055574, A067130, A058073.

Sequence in context: A067243 A171668 A259676 * A055574 A294173 A176687

Adjacent sequences: A227301 A227302 A227303 * A227305 A227306 A227307

Keyword

nonn

Author

Alex Ratushnyak, Jul 05 2013

Status

approved