A053229 Numbers n for which second differences of sigma(n) are negative.
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
Offset: 1
Keywords
Links
- G. C. Greubel, Table of n, a(n) for n = 1..10000
Programs
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Maple
with(numtheory): seq(`if`(sigma(i+2)-sigma(i+1)<(sigma(i+1)-sigma(i)),i,print( )),i=1..133);
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Mathematica
Select[Range[150], DivisorSigma[1, # + 2] - DivisorSigma[1, # + 1] < (DivisorSigma[1, # + 1] - DivisorSigma[1, #]) &] (* G. C. Greubel, Sep 03 2018 *)