A053229 - OEIS

%I #9 Oct 27 2023 22:00:45

%S 1,3,5,7,9,11,13,15,17,19,21,23,25,27,29,31,33,35,37,39,41,43,45,47,

%T 49,51,53,55,57,59,61,63,65,67,69,71,73,75,77,79,81,83,85,87,89,91,93,

%U 95,97,99,101,103,104,105,107,109,111,113,115,117,119,121,123,125,127,129

%N Numbers n for which second differences of sigma(n) are negative.

%H G. C. Greubel, <a href="/A053229/b053229.txt">Table of n, a(n) for n = 1..10000</a>

%p with(numtheory): seq(`if`(sigma(i+2)-sigma(i+1)<(sigma(i+1)-sigma(i)),i,print( )),i=1..133);

%t Select[Range[150], DivisorSigma[1, # + 2] - DivisorSigma[1, # + 1] < (DivisorSigma[1, # + 1] - DivisorSigma[1, #]) &] (* _G. C. Greubel_, Sep 03 2018 *)

%Y Cf. A000203, A053223, A053228.

%K nonn

%O 1,2

%A _Asher Auel_, Dec 10 2000