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A053228
n for which second differences of sigma(n) are positive.
5
2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64, 66, 68, 70, 72, 74, 76, 78, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98, 100, 102, 106, 108, 110, 112, 114, 116, 118, 120, 122, 124, 126, 128, 130, 132
OFFSET
1,1
LINKS
MAPLE
with(numtheory): seq(`if`(sigma(i+2)-sigma(i+1)>(sigma(i+1)-sigma(i)), i, print( )), i=1..142);
MATHEMATICA
Select[Range[150], DivisorSigma[1, #+2] - DivisorSigma[1, #+1] > (DivisorSigma[1, # + 1] - DivisorSigma[1, #]) &] (* G. C. Greubel, Sep 03 2018 *)
Position[Differences[#, 2]&/@Partition[DivisorSigma[1, Range[140]], 3, 1], _?(Positive[ #]&)][[All, 1]] (* Harvey P. Dale, Jan 18 2023 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Asher Auel, Jan 10 2000
STATUS
approved