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 A387163 #19 Aug 29 2025 10:15:25
%S A387163 10065440,12794600,22862840,24806600,27399680,30692480,33904640,
%T A387163 41629280,41851040,46803680,54625760,54842480,70384160,81915680,
%U A387163 83545280,87311840,91571480,93964640,95221280,98030240,101978240,103527200,106719200,110116160,121983680,122904320,137106200,137359040,143195360,143638880,144491200
%N A387163 Numbers k such that sigma(k) >= 3*k and A324644(k)/A324198(k) = 3.
%C A387163 This sequence contains all 3-perfect numbers (A005820) that are not multiples of three: 459818240 (= a(99)), 51001180160, and also any such hypothetical triperfects of the form 4u+2, when 2u+1 is not multiple of 3. See comments in A351458.
%H A387163 Antti Karttunen, <a href="/A387163/b387163.txt">Table of n, a(n) for n = 1..1268</a> (terms < 2^33).
%H A387163 <a href="/index/Pri#primorialbase">Index entries for sequences related to primorial base</a>
%H A387163 <a href="/index/Si#SIGMAN">Index entries for sequences related to sigma(n)</a>
%F A387163 {k | sigma(k) >= 3*k, A324644(k) = 3*A324198(k)}.
%o A387163 (PARI)
%o A387163 A276086(n) = { my(m=1, p=2); while(n, m *= (p^(n%p)); n = n\p; p = nextprime(1+p)); (m); };
%o A387163 is_A387163(n) = if(sigma(n)<3*n, 0, my(u=A276086(n)); (gcd(sigma(n), u)==3*gcd(n, u)));
%Y A387163 Intersection of A023197 and A387161.
%Y A387163 Cf. A000203, A005820, A276086, A324198, A324644, A351458.
%Y A387163 Cf. also A387165.
%K A387163 nonn,less,new
%O A387163 1,1
%A A387163 _Antti Karttunen_, Aug 28 2025