%I #22 Apr 13 2020 12:40:02
%S 2,3,23,1967,3263,5015,60455,1016507,4420163,12055511,14365607,
%T 25726727,27896423,66562307,72764735,98734967,175186655,224868311,
%U 253694927,288657203,386668343,421575407,504737747,630645455,1493547999
%N Numbers n such that sigma(n) = sigma(n+1) - sigma(n-1).
%H Donovan Johnson and Giovanni Resta, <a href="/A076530/b076530.txt">Table of n, a(n) for n = 1..112</a> (terms < 10^13, first 50 terms from Donovan Johnson)
%F a(n) = A065900(n) - 1 = A104149(n) + 1. - _Alex Ratushnyak_, Jul 06 2013
%e sigma(24) = 60. sigma(23) = 24. sigma(22) = 36 and 24 = 60 - 36; hence 23 is a term of the sequence.
%t Select[Range[2, 10^5], DivisorSigma[1, # ] == DivisorSigma[1, # + 1] - DivisorSigma[1, # - 1] &]
%t Flatten[Position[Partition[DivisorSigma[1,Range[1493548000]],3,1],_?(#[[2]] == #[[3]]-#[[1]]&),1,Heads->False]]+1 (* _Harvey P. Dale_, Apr 13 2020 *)
%Y Cf. A000203, A065900, A104149.
%K nonn
%O 1,1
%A _Joseph L. Pe_, Oct 18 2002
%E a(8)-a(25) from _Donovan Johnson_, Feb 01 2009
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