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 A120828 #19 Apr 18 2025 13:02:08
%S A120828 3,5,35,139,153,253,1053,2015,3703,6933,8173,11959
%N A120828 Numbers k such that the concatenation of n successive descending digits (1,0,9,8,7,...) starting with 1 is prime.
%C A120828 Digits are in descending order beginning with 1 and after 0 comes 9.
%C A120828 Terms must end in 3, 5 or 9. - _Michael S. Branicky_, May 11 2023
%C A120828 a(13) > 10^5. - _Michael S. Branicky_, Apr 18 2025
%e A120828 5 is a term since 10987 is a prime.
%p A120828 filter:= proc(n) local i; isprime( add(10^(n-1-i)*(1-i mod 10), i=0..n-1)) end proc:
%p A120828 select(filter, [$1..4000]); # _Robert Israel_, Mar 08 2023
%t A120828 fQ[n_] := PrimeQ@ FromDigits@ Mod[2-Range@n, 10]; lst = {}; Do[ If[fQ@n, AppendTo[lst, n]; Print@n], {n, 6000}]; lst
%Y A120828 Cf. A120804, A120819, A120829.
%K A120828 nonn,base,hard,more
%O A120828 1,1
%A A120828 _Robert G. Wilson v_, Jul 05 2006
%E A120828 Name corrected by _Robert Israel_, Mar 08 2023
%E A120828 a(10)-a(12) from _Michael S. Branicky_, May 11 2023