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 A099664 #10 Jun 29 2025 01:50:57
%S A099664 3,43,443,4441,44417,444443,4444409,44444399,444444443,4444444429,
%T A099664 44444444441,444444444443,4444444444439,44444444444353,
%U A099664 444444444444421,4444444444444423,44444444444444411,444444444444444419
%N A099664 a(n) is the largest prime before A002278(n).
%H A099664 Harvey P. Dale, <a href="/A099664/b099664.txt">Table of n, a(n) for n = 1..1000</a>
%e A099664 n=2: 43 is before 44.
%t A099664 <<NumberTheory`NumberTheoryFunctions` Table[PreviousPrime[4*(10^n-1)/9], {n, 1, 35}]
%t A099664 Table[NextPrime[FromDigits[PadRight[{},n,4]],-1],{n,20}] (* _Harvey P. Dale_, Feb 25 2013 *)
%Y A099664 Cf. A003618, A003617, A096497, A096498, A068104, A002275-A002283, A099656-A099668.
%K A099664 base,nonn
%O A099664 1,1
%A A099664 _Labos Elemer_, Nov 17 2004