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 A216473 #33 Jun 01 2017 04:36:59
%S A216473 1,3,0,6,9,2,6,0,16,18,6,22,0,27,28,15,6,0,3,6,5,21,0,46,42,48,13,0,
%T A216473 18,58,60,18,0,33,66,35,8,0,6,13,81,41,0,84,44,6,15,0,96,18,4,34,0,53,
%U A216473 108,3,112,0,18,48,22,15,0,42,21,130,18,0,8,46,138,6,0
%N A216473 a(n) = smallest m such that 2n-1 | (10^m-1)/9, or 0 if no such m exists.
%C A216473 a(n) is the multiplicative order of 10 mod 9*(2n-1) if defined, otherwise 0.
%t A216473 Table[s = MultiplicativeOrder[10, 9*(2*n - 1)]; If[! IntegerQ[s], 0, s], {n, 100}] (* _T. D. Noe_, Sep 20 2012 *)
%o A216473 (PARI) A216473(n)=if(n%5-3,znorder(Mod(10,18*n-9))) \\ _M. F. Hasler_, Sep 29 2012
%o A216473 (PARI) for(i=0,200,i++;if(i%5==0,print1(0","),print1(znorder(Mod(10,9*i))","))) \\ _V. Raman_, Nov 22 2012
%o A216473 (PARI) for(i=0,200,i++;m=0;for(x=1,i,if(((10^x-1)/9)%i==0,m=x;break));print1(m",")) \\ _V. Raman_, Nov 22 2012
%Y A216473 Cf. A002326.
%K A216473 nonn
%O A216473 1,2
%A A216473 _V. Raman_, Sep 07 2012
%E A216473 Definition corrected by _V. Raman_, Sep 20 2012