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 A090517 #7 Jul 09 2018 23:02:05
%S A090517 2,9,12,13,28,19,7,27,12,13,17,74,17,14,82,66,36,44,9,36,21,13,9,90,7,
%T A090517 19,149,51,321,35,12,14,140,13,28,42,34,36,153,155,133,46,73,106,162,
%U A090517 109,122,42,62,422,29,231,38,34,340,295,151,197,94,19,17,83,131,66,36
%N A090517 Least k such that floor[(10^n)/k] is prime.
%e A090517 a(1) = 2 as 10/2 = 5 is a prime. a(3) = 12 as floor[1000/12] = 83 is prime.
%t A090517 lkp[n_]:=Module[{k=2,c=10^n},While[!PrimeQ[Floor[c/k]],k++];k]; Array[ lkp,70] (* _Harvey P. Dale_, Jul 09 2018 *)
%Y A090517 Cf. A090518, A090519, A090520.
%K A090517 base,nonn
%O A090517 1,1
%A A090517 _Amarnath Murthy_, Dec 07 2003
%E A090517 Corrected and extended by Mohammed Bouayoun (bouyao(AT)wanadoo.fr), Jan 28 2004
%E A090517 Further terms from _David Wasserman_, Dec 20 2005