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 A068400 #28 Jun 29 2025 03:35:09
%S A068400 248,357,1045,3596,3956,4064,5396,8636,20026,20320,23374,24871,25714,
%T A068400 29029,33915,35074,39585,41656,50065,55154,56134,56536,58435,61344,
%U A068400 64285,74613,79000,87087,87685,137885,140335,142240,353133,383656,393104,423657,474548,479864
%N A068400 Numbers k such that sigma(k) = phi(k*bigomega(k)).
%C A068400 For all the numbers listed, gcd(n!-1,2^n+1) = 2n+1. Is this always true? - _Giovanni Resta_, Nov 15 2006
%C A068400 This is plausible and true for n up to 45000. - _Max Alekseyev_, Nov 16 2006
%H A068400 Amiram Eldar, <a href="/A068400/b068400.txt">Table of n, a(n) for n = 1..1000</a>
%e A068400 248 = 31*2^3 is here because sigma(248) = 480 = eulerphi(248*bigomega(2^3 * 31)) = eulerphi(248*4). - _David A. Corneth_, Jun 29 2025
%o A068400 (PARI) isok(k) = {my(f = factor(k)); sigma(f) == eulerphi(k * bigomega(f));} \\ _Amiram Eldar_, May 09 2025
%Y A068400 Cf. A000010 (phi), A000203 (sigma), A001222 (bigomega), A074891.
%K A068400 nonn
%O A068400 1,1
%A A068400 _Benoit Cloitre_, Mar 02 2002