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%I #15 Feb 11 2014 19:05:26
%S 309,425,2135,2913,6861,20155,37415,45155,74875,329841,4720281,
%T 6385749,7030911,11606649,13954745,20920075,22436225,22937785,
%U 37760631,38748291,81607505,85815925,95375589,114195965,115314295,122491401,132765639
%N Numbers n such that sigma(n-1) + sigma(n+1) = sigma(2n).
%C Conjecture: sequence contains odd values only. - _Benoit Cloitre_, Feb 18 2002
%H Donovan Johnson, <a href="/A067730/b067730.txt">Table of n, a(n) for n = 1..100</a>
%e sigma(309-1) + sigma(309+1) = 672+576 = sigma(2*309), so 309 is a term of the sequence.
%t Select[Range[10^6], DivisorSigma[1, # - 1] + DivisorSigma[1, # + 1] == DivisorSigma[1, 2# ] &]
%o (PARI) a067730(m) = for(n=2,m, if(sigma(n-1)+sigma(n+1)==sigma(2*n), print1(n,","))) a067730(10^7)
%K nonn
%O 1,1
%A _Joseph L. Pe_, Feb 05 2002
%E More terms from _Klaus Brockhaus_, Feb 07 2002
%E Edited and extended by _Robert G. Wilson v_, Feb 08 2002
%E a(21)-a(27) from _Donovan Johnson_, Jan 31 2009
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