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 A163117 #7 May 25 2019 11:04:53
%S A163117 1,1,1,3,1,7,1,9,2,3,2,9,3,1,3,7,4,1,4,3,4,7,5,3,5,9,6,1,6,7,7,1,7,3,
%T A163117 7,9,8,3,8,9,9,7,0,0,0,1,0,1,0,2,0,3,0,3,0,3,0,4,0,5,0,6,0,6,0,6,0,8,
%U A163117 0,9,0,9,0,9,1,0,1,0,1,1,1,2,1,2,1,5,1,5,1,6,1,7,1,8,1,8,1,9,2,0,2,1,2,1,2
%N A163117 The pairs of central digits of all primes with an even number of digits.
%C A163117 A subsequence of A033308.
%H A163117 Harvey P. Dale, <a href="/A163117/b163117.txt">Table of n, a(n) for n = 1..2000</a>
%e A163117 a(1)=1 and a(2)=1 represent the two digits of 11.
%e A163117 a(7)=1 and a(8)=9 represent the two digits of 19.
%e A163117 a(43)=0 and a(44)=0 represent the two zeros of the prime 1009.
%t A163117 cd[n_]:=Module[{idn=IntegerDigits[n],len},len=IntegerLength[n]/2;Take[ idn,{len,len+1}]]; cd/@Select[Prime[Range[200]],EvenQ[ IntegerLength[ #]]&]//Flatten (* _Harvey P. Dale_, Jul 23 2018 *)
%Y A163117 Cf. A093339, A162908.
%K A163117 nonn,base,less
%O A163117 1,4
%A A163117 _Juri-Stepan Gerasimov_, Jul 21 2009
%E A163117 a(8) corrected by _R. J. Mathar_, Jul 27 2009