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 A053229 Numbers n for which second differences of sigma(n) are negative. 4
 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, 53, 55, 57, 59, 61, 63, 65, 67, 69, 71, 73, 75, 77, 79, 81, 83, 85, 87, 89, 91, 93, 95, 97, 99, 101, 103, 104, 105, 107, 109, 111, 113, 115, 117, 119, 121, 123, 125, 127, 129 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS G. C. Greubel, Table of n, a(n) for n = 1..10000 MAPLE with(numtheory): seq(`if`(sigma(i+2)-sigma(i+1)<(sigma(i+1)-sigma(i)), i, print( )), i=1..133); MATHEMATICA Select[Range[150], DivisorSigma[1, # + 2] - DivisorSigma[1, # + 1] < (DivisorSigma[1, # + 1] - DivisorSigma[1, #]) &] (* G. C. Greubel, Sep 03 2018 *) CROSSREFS Cf. A000203, A053223, A053228. Sequence in context: A064679 A081874 A165747 * A157142 A247328 A317107 Adjacent sequences:  A053226 A053227 A053228 * A053230 A053231 A053232 KEYWORD nonn AUTHOR Asher Auel (asher.auel(AT)reed.edu), Dec 10 2000 STATUS approved

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Last modified January 19 06:28 EST 2021. Contains 340266 sequences. (Running on oeis4.)