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 A325638 #33 Jun 26 2024 06:01:29 %S A325638 6,28,456,496,6552,8128,30240,31452,32760,429240,2178540,7505976, %T A325638 23569920,33550336,45532800,142990848,1379454720 %N A325638 Numbers m such that sigma(m) can be obtained as the base-2 carryless product of 2m and some k. %C A325638 Numbers m such that A000203(m) = A048720(2m, k) for some k. %C A325638 Numbers m for which A091255(2m, sigma(m)) = 2m. %C A325638 Conjecture: all terms are even. If this is true, then there are no odd perfect numbers. See also conjectures in A325639 and in A325808. %H A325638 <a href="/index/Ca#CARRYLESS">Index entries for sequences related to carryless arithmetic</a>. %H A325638 <a href="/index/Si#SIGMAN">Index entries for sequences related to sigma(n)</a>. %H A325638 <a href="/index/O#opnseqs">Index entries for sequences where any odd perfect numbers must occur</a>. %o A325638 (PARI) %o A325638 A091255sq(a,b) = fromdigits(Vec(lift(gcd(Pol(binary(a))*Mod(1, 2),Pol(binary(b))*Mod(1, 2)))),2); %o A325638 A325635(n) = A091255sq(n+n, sigma(n)); %o A325638 isA325638(n) = ((n+n)==A325635(n)); %Y A325638 Cf. A000203, A091255, A325635, A325637, A325808. %Y A325638 Subsequence of A325639. %Y A325638 Cf. A000396 (a subsequence). %K A325638 nonn,more %O A325638 1,1 %A A325638 _Antti Karttunen_, May 21 2019 %E A325638 a(17) from _Amiram Eldar_, Jun 26 2024