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 A275671 #18 Dec 26 2024 03:51:37 %S A275671 4,6,8,12,14,18,20,24,28,30,32,36,38,40,42,44,48,54,56,60,62,68,72,74, %T A275671 78,80,84,90,96,98,102,104,108,110,112,114,120,124,126,128,132,138, %U A275671 140,144,150,152,156,158,160,162,164,168,174,176,180,182,186,192,194 %N A275671 Even values produced by the sigma function A000203, in increasing order. %C A275671 Even terms of A002191. %C A275671 Complement of A060657 with respect to A002191. %H A275671 Amiram Eldar, <a href="/A275671/b275671.txt">Table of n, a(n) for n = 1..10000</a> %H A275671 Max Alekseyev, <a href="https://oeis.org/wiki/User:Max_Alekseyev/gpscripts">PARI/GP Scripts for Miscellaneous Math Problems</a> (invphi.gp). %e A275671 8 is in the sequence because sigma(7) = 8 and it is an even number. %o A275671 (Magma) Set(Sort([SumOfDivisors(n): n in[1..1000] | not IsOdd(SumOfDivisors(n)) and SumOfDivisors(n) le 1000])); %o A275671 (PARI) is(k) = !(k % 2) && invsigmaNum(k) > 0; \\ _Amiram Eldar_, Dec 26 2024, using _Max Alekseyev_'s invphi.gp %Y A275671 Cf. A000203, A002191, A060657, A152678. %K A275671 nonn %O A275671 1,1 %A A275671 _Jaroslav Krizek_, Aug 04 2016