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 A343216 #14 Aug 30 2025 10:25:39
%S A343216 1,2,4,9,13,16,18,25,36,37,49,50,61,64,73,81,97,100,101,109,113,121,
%T A343216 137,144,157,169,173,181,193,225,229,241,242,256,257,277,281,289,313,
%U A343216 317,324,325,333,337,353,361,373,397,400,401,409,421,433,441,457,484,512,529,541,549,576,577,578,601,613,617,625,641
%N A343216 Numbers k such that A003415(sigma(k)) < k, where A003415(x) gives the arithmetic derivative of x.
%H A343216 Antti Karttunen, <a href="/A343216/b343216.txt">Table of n, a(n) for n = 1..10000</a>
%H A343216 <a href="/index/Si#SIGMAN">Index entries for sequences related to sigma(n)</a>
%t A343216 Select[Range[641], If[#2 < 2, 0, #2 Total[#2/#1 & @@@ FactorInteger[#2]]] < #1 & @@ {#, DivisorSigma[1, #]} &] (* _Michael De Vlieger_, Apr 08 2021 *)
%o A343216 (PARI)
%o A343216 A003415(n) = if(n<=1, 0, my(f=factor(n)); n*sum(i=1, #f~, f[i, 2]/f[i, 1]));
%o A343216 isA343216(n) = (A003415(sigma(n))<n);
%Y A343216 Cf. A000203, A003415, A343217 (complement), A342925.
%Y A343216 Positions of negative terms in A342926.
%K A343216 nonn,changed
%O A343216 1,2
%A A343216 _Antti Karttunen_, Apr 08 2021