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 A113619 #26 Feb 16 2025 08:32:59
%S A113619 1,2,3,4,5,6,8,9,10,11,12,13,15,16,17,19,20,22,23,24,25,26,27,29,30,
%T A113619 31,32,33,37,38,39,40,41,43,44,45,46,47,48,50,51,52,53,57,58,59,60,61,
%U A113619 62,64,65,66,67,69,71,73,74,75,76,78,79,80,82,83,85,86,87,88,89,92,93,94,95,96,97,99,100
%N A113619 Heptagon-free numbers: numbers k such that no divisor of k is a heptagonal number > 1.
%C A113619 Heptagonal number analogy of A112886 (the triangle-free positive integers).
%H A113619 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/HeptagonalNumber.html">Heptagonal Number.</a>
%e A113619 7 is the first nontrivial heptagonal number, so no multiple of 7 is a term.
%t A113619 upto=100;Module[{maxhep=Floor[(3+Sqrt[9+40upto])/10],heps}, heps= Rest[ Table[(n(5n-3))/2,{n,maxhep}]];Complement[Range[upto],Union[ Flatten[ Table[n*heps,{n,Ceiling[upto/7]}]]]]] (* _Harvey P. Dale_, May 19 2012 *)
%Y A113619 Cf. A000566, A112886, A113502.
%K A113619 easy,nonn
%O A113619 1,2
%A A113619 _Jonathan Vos Post_, Jan 14 2006
%E A113619 Corrected by _Harvey P. Dale_, May 19 2012