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 A067730 Numbers n such that sigma(n-1) + sigma(n+1) = sigma(2n). 3
 309, 425, 2135, 2913, 6861, 20155, 37415, 45155, 74875, 329841, 4720281, 6385749, 7030911, 11606649, 13954745, 20920075, 22436225, 22937785, 37760631, 38748291, 81607505, 85815925, 95375589, 114195965, 115314295, 122491401, 132765639 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Conjecture: sequence contains odd values only. - Benoit Cloitre, Feb 18 2002 LINKS Donovan Johnson, Table of n, a(n) for n = 1..100 EXAMPLE sigma(309-1) + sigma(309+1) = 672+576 = sigma(2*309), so 309 is a term of the sequence. MATHEMATICA Select[Range[10^6], DivisorSigma[1, # - 1] + DivisorSigma[1, # + 1] == DivisorSigma[1, 2# ] &] PROG (PARI) a067730(m) = for(n=2, m, if(sigma(n-1)+sigma(n+1)==sigma(2*n), print1(n, ", "))) a067730(10^7) CROSSREFS Sequence in context: A060980 A061881 A121322 * A183627 A184544 A251345 Adjacent sequences:  A067727 A067728 A067729 * A067731 A067732 A067733 KEYWORD nonn AUTHOR Joseph L. Pe, Feb 05 2002 EXTENSIONS More terms from Klaus Brockhaus, Feb 07 2002 Edited and extended by Robert G. Wilson v, Feb 08 2002 a(21)-a(27) from Donovan Johnson, Jan 31 2009 STATUS approved

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Last modified August 10 12:39 EDT 2020. Contains 336379 sequences. (Running on oeis4.)