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 A135697 #15 Dec 09 2024 09:28:33
%S A135697 3,33,313,3113,31413,314413,3141413,31411413,314151413,3141551413,
%T A135697 31415951413,314159951413,3141592951413,31415922951413,
%U A135697 314159262951413,3141592662951413,31415926562951413,314159265562951413,3141592653562951413,31415926533562951413,314159265353562951413
%N A135697 Palindromes formed from the reflected decimal expansion of Pi.
%C A135697 Pi = 3.14159265358979323846264338327... (see A000796).
%C A135697 The number of digits of a(n) is equal to n.
%H A135697 Paolo Xausa, <a href="/A135697/b135697.txt">Table of n, a(n) for n = 1..900</a>
%e A135697 n Digits of a(n)
%e A135697 1 ( 3 )
%e A135697 2 ( 3 3 )
%e A135697 3 ( 3 1 3 )
%e A135697 4 ( 3 1 1 3 )
%e A135697 5 ( 3 1 4 1 3 )
%e A135697 6 ( 3 1 4 4 1 3 )
%e A135697 7 ( 3 1 4 1 4 1 3 )
%e A135697 8 ( 3 1 4 1 1 4 1 3 )
%e A135697 9 ( 3 1 4 1 5 1 4 1 3 )
%e A135697 10 ( 3 1 4 1 5 5 1 4 1 3 )
%t A135697 Table[FromDigits[Join[#[[;; Floor[n/2]]], #[[Ceiling[n/2] ;; 1 ;; -1]]]], {n, Length[#]}] & [First[RealDigits[Pi, 10, 25]]] (* _Paolo Xausa_, Dec 09 2024 *)
%Y A135697 Cf. A000796, A002113, A039954, A138070, A138071.
%K A135697 base,nonn
%O A135697 1,1
%A A135697 _Omar E. Pol_, Mar 01 2008, Mar 28 2008