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A067828
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Odd numbers k such that sigma(k+1) < sigma(k).
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3
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45, 105, 117, 165, 225, 273, 297, 315, 345, 357, 405, 465, 513, 525, 561, 585, 621, 693, 705, 765, 777, 825, 837, 861, 885, 945, 1005, 1113, 1125, 1155, 1185, 1197, 1281, 1305, 1365, 1395, 1425, 1485, 1521, 1545, 1575, 1593, 1617, 1701, 1725, 1755, 1785, 1845
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OFFSET
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1,1
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COMMENTS
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Most terms are == 3 (mod 6), first term == 1 (mod 6) is a(130) = 5005. First term == 5 (mod 6) may be 247818996425. - Jianing Song, Apr 01 2018
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LINKS
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MATHEMATICA
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Select[Range[1, 2000, 2], DivisorSigma[1, #] > DivisorSigma[1, # + 1] &] (* Amiram Eldar, Jun 06 2022 *)
Select[Flatten[Position[Partition[DivisorSigma[1, Range[2000]], 2, 1], _?(#[[2]]<#[[1]]&), 1, Heads-> False]], OddQ] (* Harvey P. Dale, Aug 02 2024 *)
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PROG
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(PARI) isok(n) = (n % 2) && (sigma(n+1) < sigma(n)); \\ Michel Marcus, Nov 23 2013
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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