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 A099663 #17 Jun 29 2025 09:05:01
%S A099663 19,211,2221,22193,222199,2222219,22222199,222222193,2222222137,
%T A099663 22222222189,222222222169,2222222222197,22222222222201,
%U A099663 222222222222151,2222222222222203,22222222222222153,222222222222222221,2222222222222222177,22222222222222222169,222222222222222222149,2222222222222222222161
%N A099663 a(n) is the largest prime before A002276(n).
%F A099663 a(n) = A007917(A002276(n)). - _Michel Marcus_, Jun 29 2025
%e A099663 n=2: 19 is before 22.
%t A099663 Table[NextPrime[2(10^n-1)/9, -1], {n, 2, 35}]
%t A099663 Drop[NextPrime[#,-1]&/@LinearRecurrence[{11,-10},{0,2},20],2] (* _Harvey P. Dale_, Dec 19 2020 *)
%Y A099663 Cf. A007917, A002276.
%Y A099663 Cf. A003618, A003617, A096497, A096498, A068104, A002275-A002283, A099656-A099669.
%K A099663 base,nonn
%O A099663 2,1
%A A099663 _Labos Elemer_, Nov 17 2004
%E A099663 More terms from _Michel Marcus_, Jun 29 2025