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 A099081 #13 Sep 14 2024 10:49:35
%S A099081 1,2,6,30,88
%N A099081 Numbers k such that 1.2. ... .k-1.k + 1 is prime (where dot between numbers means concatenation).
%C A099081 a(6) > 25000. - _Michael S. Branicky_, Sep 13 2024
%e A099081 6 is in the sequence because 123456+1 is prime.
%t A099081 f[n_] := Block[{p = 0, k = 1}, While[k <= n, p = 10^Floor[ Log[10, k] + 1]p + k; k++ ]; PrimeQ[p + 1]]; Do[ If[ f[n], Print[n]], {n, 1000}] (* _Robert G. Wilson v_, Nov 01 2004 *)
%Y A099081 Cf. A099082, A099083.
%K A099081 base,more,nonn
%O A099081 1,2
%A A099081 _Farideh Firoozbakht_, Oct 23 2004