This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A087415 #15 Mar 02 2025 08:00:08
%S A087415 1,315,945,1155,2205,7425,8415,8925,9405,9555,24885,26145,26325,28035,
%T A087415 30555,31815,32445,33705,34335,35595,40005,40365,41265,43155,46035,
%U A087415 49875,51765,55335,78975,80535,83265,91455,96915,101475,106425,130815,191565,338415
%N A087415 Odd numbers k such that abs(sigma(k)-2k) <= sqrt(k). Abundance-radius = abs(sigma(k)-2k) does not exceed square root of k and k is odd.
%H A087415 Donovan Johnson, <a href="/A087415/b087415.txt">Table of n, a(n) for n = 1..1000</a>
%t A087415 abu[x_] := Abs[DivisorSigma[1, x]-2*x]; Do[If[ !Greater[abu[n], Sqrt[n]//N]&& OddQ[n], Print[n]], {n, 1, 100000}]
%o A087415 (PARI) isok(k) = k % 2 && (sigma(k)-2*k)^2 <= k; \\ _Amiram Eldar_, Mar 02 2025
%Y A087415 Intersection of A005408 and A088007.
%Y A087415 Cf. A077374, A088008-A088012, A000396, A000079, A005100, A005101.
%K A087415 nonn
%O A087415 1,2
%A A087415 _Labos Elemer_, Oct 20 2003