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 A099667 #19 Sep 01 2017 09:56:08
%S A099667 5,73,773,7759,77773,777769,7777769,77777761,777777773,7777777741,
%T A099667 77777777767,777777777773,7777777777771,77777777777753,
%U A099667 777777777777773,7777777777777753,77777777777777747,777777777777777743
%N A099667 a(n) is the largest prime before A002281(n); repdigits repeating 7.
%H A099667 Michael De Vlieger, <a href="/A099667/b099667.txt">Table of n, a(n) for n = 1..1000</a>
%e A099667 n=2: 73 is before 77.
%t A099667 Table[NextPrime[7 (10^n - 1)/9, -1], {n, 35}]
%t A099667 (* Second program: *)
%t A099667 Rest[NextPrime[#,-1]&/@LinearRecurrence[{11,-10},{0,7},25]] (* _Harvey P. Dale_, May 24 2015 *)
%Y A099667 Cf. A003618, A003617, A096497, A096498, A068104, A002275-A002283, A099656-A099668.
%K A099667 base,nonn
%O A099667 1,1
%A A099667 _Labos Elemer_, Nov 17 2004
%E A099667 Name changed by _David A. Corneth_, Sep 01 2017