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 A325639 #17 Jun 17 2019 18:01:50 %S A325639 1,6,28,120,312,428,456,496,504,672,760,6552,8128,30240,31452,32760, %T A325639 429240,523776,2178540,5009850,7505976,23569920,33550336,45532800, %U A325639 142990848,186076800,379975680 %N A325639 Numbers n for which A091255(n, sigma(n)) = n. %C A325639 Numbers n for which A000203(n) = A048720(n, k) for some k. The value of k for the initial terms is: 1, 2, 2, 7, 3, 3, 6, 2, 5, 3, 3, 6, 2, 4, 6, 4, 6, 7, 4, 3, 6, 4, 2, 4, 4, 7, 7, ... %C A325639 Conjecture: all terms after the initial one are even. If this is true, then there are no odd perfect numbers. %C A325639 A007691(11) = 2178540 is the first term of A007691 which is not present in this sequence. %H A325639 <a href="/index/O#opnseqs">Index entries for sequences where any odd perfect numbers must occur</a> %o A325639 (PARI) %o A325639 A091255sq(a,b) = fromdigits(Vec(lift(gcd(Pol(binary(a))*Mod(1, 2),Pol(binary(b))*Mod(1, 2)))),2); %o A325639 A325634(n) = A091255sq(n, sigma(n)); %o A325639 isA325639(n) = (A325634(n)==n); %Y A325639 Fixed points of A325632 and A325634. %Y A325639 Cf. A000203, A007691, A048720, A091255. %Y A325639 Cf. A000396, A325638 (subsequences). %K A325639 nonn,more %O A325639 1,2 %A A325639 _Antti Karttunen_, May 21 2019