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 A109445 #13 Aug 28 2025 10:20:47
%S A109445 4,8,10,42,452,1014
%N A109445 Numbers k such that (concatenation of even integers through k) - 1 is a prime.
%C A109445 Next term is greater than 2000. All terms less than 1000 correspond to certified primes (Primo 2.2.0 beta).
%C A109445 Next term is greater than 20000. - _Michael S. Branicky_, Aug 28 2025
%e A109445 4 is a term because 24 - 1 = 23 is prime.
%e A109445 8 is a term because 2468 - 1 = 2467 is prime.
%t A109445 p = ""; Do[p = p <> ToString[2*n]; If[PrimeQ[ToExpression[p] - 1], Print[2*n]], {n, 1, 10^3}]
%Y A109445 Cf. A066811.
%K A109445 base,nonn,more,changed
%O A109445 1,1
%A A109445 _Ryan Propper_, Aug 26 2005