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A103288 Numbers k such that sigma(k) >= 2k-1 (union of perfect, abundant and least deficient numbers).

%I A103288 #17 Dec 09 2024 11:02:20
%S A103288 1,2,4,6,8,12,16,18,20,24,28,30,32,36,40,42,48,54,56,60,64,66,70,72,
%T A103288 78,80,84,88,90,96,100,102,104,108,112,114,120,126,128,132,138,140,
%U A103288 144,150,156,160,162,168,174,176,180,186,192,196,198,200,204,208,210,216,220
%N A103288 Numbers k such that sigma(k) >= 2k-1 (union of perfect, abundant and least deficient numbers).
%C A103288 If the only least deficient numbers are the powers of 2 (open problem) then this sequence is the union of A023196 and A000079.
%C A103288 Like the abundant numbers, this sequence has density between 0.2474 and 0.2480, see A005101. - _Charles R Greathouse IV_, Nov 30 2022
%H A103288 Paolo Xausa, <a href="/A103288/b103288.txt">Table of n, a(n) for n = 1..10000</a> (terms 1..1000 from T. D. Noe)
%F A103288 Numbers k such that A004125(k) <= A004125(k-1).
%t A103288 Select[Range[500], DivisorSigma[1, #] >= 2*# - 1 &] (* _Paolo Xausa_, Dec 09 2024 *)
%o A103288 (PARI) for(n=1,1000,if(sigma(n)>=2*n-1,print(n)));
%Y A103288 Cf. A023196, A023197, A023198, A023199, A000079, A004125.
%K A103288 nonn
%O A103288 1,2
%A A103288 _Max Alekseyev_, Jan 28 2005