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 A384840 #12 Jun 12 2025 14:25:05 %S A384840 1952,1992,2016,2160,2520,2640,3314,3744,3801,4320,4484,4500,4566, %T A384840 4620,4680,4994,5016,5948,6072,6096,6194,6384,6492,6552,6654,6870, %U A384840 7056,7200,7224,7382,7435,7440,7470,7794,7812,7920,7956,8376,8480,8604,8616,8702,8892,9284,9360,9408 %N A384840 Numbers k for which sigma(k - x) + sigma(k + x) = 7*k has at least one nonnegative solution. %H A384840 Michel Marcus, <a href="/A384840/b384840.txt">Table of n, a(n) for n = 1..1000</a> %o A384840 (PARI) isok(k) = for (x=0, k-1, if (sigma(k - x) + sigma(k + x) == 7*k, return(1))); %Y A384840 Cf. A000203 (sigma), A055153 (a subsequence). %Y A384840 Cf. A383268, A384838, A384839, A384841. %Y A384840 Cf. A383758. %K A384840 nonn %O A384840 1,1 %A A384840 _Michel Marcus_, Jun 10 2025