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 A347880 #7 Sep 18 2021 22:05:06 %S A347880 4,5,8,14,16,20,23,25,26,30,38,41,49,51,59,62,64,66,74,77,80,86,90,92, %T A347880 96,102,108,113,120,122,124,127,131,134,138,143,146,149,153,158,159, %U A347880 164,165,167,169,174,194,196,198,200,203,204,206,209,210,213,217,218,223,236,239,243,246,254,255,257,264,267,270 %N A347880 Numbers k such that A342926(k) is a multiple of 3. %t A347880 ad[1] = 0; ad[n_] := n * Total@(Last[#]/First[#]& /@ FactorInteger[n]); Select[Range[270], Divisible[ad[DivisorSigma[1, #]] - #, 3] &] (* _Amiram Eldar_, Sep 18 2021 *) %o A347880 (PARI) %o A347880 A003415(n) = if(n<=1, 0, my(f=factor(n)); n*sum(i=1, #f~, f[i, 2]/f[i, 1])); %o A347880 A342926(n) = (A003415(sigma(n))-n); %o A347880 isA347880(n) = !(A342926(n)%3); %Y A347880 Positions of zeros in A347883. %Y A347880 Cf. A000203, A003415, A342926. %Y A347880 Cf. A005820, A342923 (subsequences). %Y A347880 Cf. also A347872. %K A347880 nonn %O A347880 1,1 %A A347880 _Antti Karttunen_, Sep 18 2021