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 A231548 #13 Nov 23 2019 02:47:45 %S A231548 1680,2520,3360,3780,3960,4200,4680,5040,6300,6720,7560,7920,8820, %T A231548 9240,9360,10080,10800,10920,11340,11760,11880,12600,13440,13860, %U A231548 14040,15120,15840,15960,16380,16800,17280,17640,18480,18900,19800,20160,20520,21000,21420 %N A231548 Numbers n such that 2*n - 1 < sigma(n) - sigma(n-2). %C A231548 Also numbers n such that antisigma(n) < antisigma(n-2), where antisigma(n) = A024816(n) = the sum of the non-divisors of n that are between 1 and n. %C A231548 Sequence contains anomalous increased frequency of values ending with digit 0. %C A231548 Conjecture: there are no numbers n such that antisigma(n) < antisigma(n-3). %H A231548 Jaroslav Krizek, <a href="/A231548/b231548.txt">Table of n, a(n) for n = 1..228, all terms < 10^5</a> %e A231548 1680 is in sequence because antisigma(1680) = 1406088 < antisigma(1678) = 1406161. %Y A231548 Cf. A024816, A213547 (numbers n such that antisigma(n) < antisigma(n-1)). %K A231548 nonn %O A231548 1,1 %A A231548 _Jaroslav Krizek_, Nov 12 2013