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A067730
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n satisfying sigma(n-1) + sigma(n+1) = sigma(2n).
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3
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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; internal format)
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OFFSET
| 1,1
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COMMENTS
| Conjecture: sequence contains odd values only - Benoit Cloitre (benoit7848c(AT)orange.fr), Feb 18 2002
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EXAMPLE
| sigma(309-1) + sigma(309+1) = 672+576= sigma(2*309), so 309 is a term of the sequence.
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MATHEMATICA
| Select[Range[10^6], DivisorSigma[1, # - 1] + DivisorSigma[1, # + 1] == DivisorSigma[1, 2# ] &]
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PROG
| (PARI) a067730(m) = for(n=2, m, if(sigma(n-1)+sigma(n+1)==sigma(2*n), print1(n, ", "))) a067730(10^7)
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CROSSREFS
| Sequence in context: A060980 A061881 A121322 * A183627 A184544 A105841
Adjacent sequences: A067727 A067728 A067729 * A067731 A067732 A067733
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KEYWORD
| nonn
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AUTHOR
| Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Feb 05 2002
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EXTENSIONS
| More terms from Klaus Brockhaus (klaus-brockhaus(AT)t-online.de), Feb 07 2002
Edited and extended by Robert G. Wilson v (rgwv(AT)rgwv.com), Feb 08 2002
a(21)-a(27) from Donovan Johnson (donovan.johnson(AT)yahoo.com), Jan 31 2009
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