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 A385075 #9 Jun 16 2025 18:13:05 %S A385075 361881,792960,835072,837312,846720,917280,944608,946176,1509236, %T A385075 1517264,1630880,1635600,1636614,1697560,1834560,1914092,1926336, %U A385075 1927692,1941264,2387120,2450112,2474316,2494464,2546656,2573088,2624832,2685394,2705680,2840468,2913120,2941009 %N A385075 Numbers k for which sigma(k - x) + sigma(k + x) = 9*k has at least one nonnegative solution. %C A385075 At least one of sigma(k - x) >= 4.5*(k - x) or sigma(k+x) >= 4.5*(k + x) is true. - _David A. Corneth_, Jun 16 2025 %H A385075 David A. Corneth, <a href="/A385075/a385075.gp.txt">PARI program</a> %e A385075 361881 is in the sequence via k = 361881 and x = 358839 so k-x = 3042, k+x = 720720 and sigma(k - x) + sigma(k + x) = 7137 + 3249792 = 3256929 = 9*361881 = 9*k. - _David A. Corneth_, Jun 16 2025 %o A385075 (PARI) isok(k) = forstep(x=k-1, 0, -1, if (sigma(k - x) + sigma(k + x) == 9*k, return(1))); %Y A385075 Cf. A000203, A141645 (a subsequence). %Y A385075 Cf. A383268, A384838, A384839, A384840, A384841. %Y A385075 Cf. A383758. %K A385075 nonn %O A385075 1,1 %A A385075 _Michel Marcus_, Jun 16 2025 %E A385075 More terms from _David A. Corneth_, Jun 16 2025