A076530 - OEIS

A076530

Numbers n such that sigma(n) = sigma(n+1) - sigma(n-1).

2, 3, 23, 1967, 3263, 5015, 60455, 1016507, 4420163, 12055511, 14365607, 25726727, 27896423, 66562307, 72764735, 98734967, 175186655, 224868311, 253694927, 288657203, 386668343, 421575407, 504737747, 630645455, 1493547999

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

LINKS

Donovan Johnson and Giovanni Resta, Table of n, a(n) for n = 1..112 (terms < 10^13, first 50 terms from Donovan Johnson)

FORMULA

a(n) = A065900(n) - 1 = A104149(n) + 1. - Alex Ratushnyak, Jul 06 2013

EXAMPLE

sigma(24) = 60. sigma(23) = 24. sigma(22) = 36 and 24 = 60 - 36; hence 23 is a term of the sequence.

MATHEMATICA

Select[Range[2, 10^5], DivisorSigma[1, # ] == DivisorSigma[1, # + 1] - DivisorSigma[1, # - 1] &]

Flatten[Position[Partition[DivisorSigma[1, Range[1493548000]], 3, 1], _?(#[[2]] == #[[3]]-#[[1]]&), 1, Heads->False]]+1 (* Harvey P. Dale, Apr 13 2020 *)

CROSSREFS

Cf. A000203, A065900, A104149.

Sequence in context: A160341 A092388 A225726 * A360225 A238265 A203015

Adjacent sequences: A076527 A076528 A076529 * A076531 A076532 A076533

KEYWORD

nonn

AUTHOR

Joseph L. Pe, Oct 18 2002

EXTENSIONS

a(8)-a(25) from Donovan Johnson, Feb 01 2009

STATUS

approved