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 A138071 #15 Dec 08 2024 16:07:16
%S A138071 3,3,1,3,3,1,4,1,3,3,1,4,1,4,1,3,3,1,4,1,5,1,4,1,3,3,1,4,1,5,9,5,1,4,
%T A138071 1,3,3,1,4,1,5,9,2,9,5,1,4,1,3,3,1,4,1,5,9,2,6,2,9,5,1,4,1,3,3,1,4,1,
%U A138071 5,9,2,6,5,6,2,9,5,1,4,1,3
%N A138071 Triangle read by rows: row n lists the digits of A135698(n), the palindromic number with odd number of digits formed from the reflected decimal expansion of Pi.
%C A138071 Also, successive digits of the numbers A135698(n).
%H A138071 Paolo Xausa, <a href="/A138071/b138071.txt">Table of n, a(n) for n = 1..10000</a> (rows 1..100 of triangle, flattened).
%e A138071 Triangle begins:
%e A138071 3
%e A138071 3, 1, 3
%e A138071 3, 1, 4, 1, 3
%e A138071 3, 1, 4, 1, 4, 1, 3
%e A138071 3, 1, 4, 1, 5, 1, 4, 1, 3
%t A138071 Table[Join[#[[;; n - 1]], #[[n ;; 1 ;; -1]]], {n, Length[#]}] & [First[RealDigits[Pi, 10, 15]]] (* _Paolo Xausa_, Dec 08 2024 *)
%Y A138071 Decimal expansion of Pi: A000796. Cf. A119351, A135697, A135698, A138070.
%K A138071 easy,nonn,tabf,base
%O A138071 1,1
%A A138071 _Omar E. Pol_, Mar 03 2008