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 A190301 #22 Nov 29 2020 01:02:57
%S A190301 1,0,37,0,0,0,15873,0,12345679,0,1,0,8547,0,0,0,65359477124183,0,
%T A190301 5847953216374269,0,5291,0,48309178743961352657,0,0,0,
%U A190301 4115226337448559670781893,0,38314176245210727969348659,0,3584229390681,0,3367,0,0,0,3,0,2849,0,271,0
%N A190301 Smallest number h such that n*h is a repunit (A002275), or 0 if no such h exists.
%H A190301 Robert G. Wilson v, <a href="/A190301/b190301.txt">Table of n, a(n) for n = 1..1001</a> (first 300 terms from T. D. Noe)
%e A190301 For n = 7: a(7) = 15873 because 7 * 15873 = 111111. Repunit 111111 is the smallest repunit with prime factor 7.
%t A190301 Table[If[GCD[n, 10] > 1, 0, k = MultiplicativeOrder[10, 9*n]; (10^k - 1)/(9*n)], {n, 100}] (* _T. D. Noe_, May 08 2011 *)
%o A190301 (PARI) a(n)=if(gcd(n,10)>1, 0, (10^znorder(Mod(10,9*n))-1)/9/n) \\ _Charles R Greathouse IV_, Aug 28 2016
%Y A190301 Cf. A084681 (repunit length), A216479 (the repunit).
%Y A190301 Cf. A050782 = the smallest number h such that n*h is palindromic number, A083117 = the smallest number h such that n*h is repdigit number.
%Y A190301 Cf. A004290, A079339, A181060, A181061.
%K A190301 nonn
%O A190301 1,3
%A A190301 _Jaroslav Krizek_, May 07 2011