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 A215258 #5 Sep 11 2012 12:25:32
%S A215258 1,37,0,15873,12345679,1,8547,0,65359477124183,5847953216374269,5291,
%T A215258 48309178743961352657,0,4115226337448559670781893,
%U A215258 38314176245210727969348659,3584229390681,3367,0,3,2849,271,2583979328165374677,0
%N A215258 Smallest number h such that (2n+1)*h is a repunit (A002275), or 0 if no such h exists.
%H A215258 T. D. Noe, <a href="/A215258/b215258.txt">Table of n, a(n) for n = 0..200</a>
%t A215258 Table[If[GCD[n, 10] > 1, 0, k = MultiplicativeOrder[10, 9*n]; (10^k - 1)/(9*n)], {n, 1, 51, 2}] (* _T. D. Noe_, Sep 11 2012 *)
%Y A215258 A bisection of A190301.
%K A215258 nonn
%O A215258 0,2
%A A215258 _N. J. A. Sloane_, Sep 11 2012