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 A349752 #15 Dec 04 2021 12:31:19 %S A349752 7,13,15,19,31,33,37,43,61,67,69,73,79,87,97,103,105,109,123,127,139, %T A349752 141,147,151,153,157,163,175,177,181,193,195,199,211,223,229,231,241, %U A349752 249,271,277,283,285,303,307,313,325,331,337,339,349,367,373,375,379,393,397,409,411,421,429,433,439,447,457,463 %N A349752 Odd numbers k for which the sigma(k) == -k (mod 3) and sigma(k) preserves the 3-adic valuation of k. %C A349752 Incidentally, of the 37 known terms of A228059, all of which are multiples of three, only 15 (less than half) satisfy this condition. %H A349752 <a href="/index/O#opnseqs">Index entries for sequences where odd perfect numbers must occur, if they exist at all</a> %H A349752 <a href="/index/Si#SIGMAN">Index entries for sequences related to sigma(n)</a> %t A349752 Select[Range[1, 463, 2], Divisible[(s = DivisorSigma[1, #]) + #, 3] && IntegerExponent[s, 3] == IntegerExponent[#, 3] &] (* _Amiram Eldar_, Dec 01 2021 *) %o A349752 (PARI) isA349752(n) = ((n%2) && (0==(sigma(n)+n)%3) && valuation(sigma(n), 3)==valuation(n, 3)); %Y A349752 Intersection of A349749 and A349751. %Y A349752 Cf. A000203, A007949, A010872, A074941, A228059, A329963, A349750. %K A349752 nonn %O A349752 1,1 %A A349752 _Antti Karttunen_, Nov 30 2021