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 A377766 #19 Jun 23 2025 14:31:44 %S A377766 4,8,32,50,98,128,242,324,338,392,722,784,800,1058,1250,1444,2304, %T A377766 2312,2450,2704,2738,3600,3872,5408,5476,5618,6272,6728,7442,7688, %U A377766 8192,9248,11552,12482,12800,14400,14884,15488,15842,16562,16900,16928,17672,18050,19208,21632,21904,22500,23762,25088 %N A377766 Even numbers whose sum of proper (or aliquot) divisors is a prime. %C A377766 Even terms of A037020. %C A377766 Numbers from A088827 (2n^2 or 4n^2) are the only aliquot sum transition from even to odd. %H A377766 Michel Marcus, <a href="/A377766/b377766.txt">Table of n, a(n) for n = 1..3000</a> %e A377766 The aliquot divisors of 32 are 1, 2, 4, 8 and 16, whose sum is 31, a prime, so 32 is a term. %t A377766 Select[2Range[13000],PrimeQ[DivisorSigma[1,#]-#] &] (* _Stefano Spezia_, Nov 08 2024 *) %o A377766 (PARI) is_a377766(n) = !(n%2) && isprime(sigma(n)-n) \\ _Hugo Pfoertner_, Nov 07 2024 %Y A377766 Intersection of A005843 and A037020. %Y A377766 Cf. A088827. %K A377766 nonn,easy %O A377766 1,1 %A A377766 _Ophir Spector_, Nov 06 2024