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 A121172 #15 Oct 13 2024 12:53:31
%S A121172 1,1,3,7,7,22,3,6,6,3,19,18,4,39,6,13,37,15,15,6,16,9,96,61,19,6,9,3,
%T A121172 33,63,57,117,55,49,30,3,28,6,42,24,36,72,21,60,6,24,33,61,21,85,31,
%U A121172 49,13,93,18,90,9,16,135,19,55,9,135,60,6,30,3,16,115,114,19,99,15,147,171,42
%N A121172 Smallest integer k>0 such that k*10^n + 1 is a prime.
%H A121172 Robert Price, <a href="/A121172/b121172.txt">Table of n, a(n) for n = 1..1000</a>
%F A121172 a(n) = (A070854(n)-1)/10^n. - _Ray Chandler_, Feb 10 2009
%e A121172 a(1) = 1 because A030430[1] = 11 is a smallest prime of form 10*k + 1.
%e A121172 a(2) = 1 because A062800[1] = 101 is a smallest prime of form 100*k + 1.
%t A121172 s={};Do[k=0;Until[PrimeQ[k*10^n+1],k++];AppendTo[s,k],{n,76}];s (* _James C. McMahon_, Oct 13 2024 *)
%Y A121172 Cf. A030430, A062800, see A070854 for resulting primes.
%K A121172 nonn
%O A121172 1,3
%A A121172 _Alexander Adamchuk_, Aug 14 2006
%E A121172 Minor edits by _Ray Chandler_, Feb 10 2009