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 A135696 #8 Oct 27 2016 03:17:08
%S A135696 2,272,27172,2718172,271828172,27182828172,2718281828172,
%T A135696 271828181828172,27182818281828172,2718281828281828172,
%U A135696 271828182848281828172,27182818284548281828172,2718281828459548281828172,271828182845909548281828172,27182818284590409548281828172
%N A135696 Palindromes with odd number of digits formed from the reflected decimal expansion of e.
%C A135696 e = 2.71828182845904523536028747135... (see A001113).
%C A135696 The number of digits of a(n) is equal to 2n-1.
%H A135696 G. C. Greubel, <a href="/A135696/b135696.txt">Table of n, a(n) for n = 1..250</a>
%e A135696 n ............ a(n)
%e A135696 1 ............. 2
%e A135696 2 ............ 272
%e A135696 3 ........... 27172
%e A135696 4 .......... 2718172
%e A135696 5 ......... 271828172
%e A135696 6 ........ 27182828172
%e A135696 7 ....... 2718281828172
%e A135696 8 ...... 271828181828172
%e A135696 9 ..... 27182818281828172
%e A135696 10 ... 2718281828281828172
%t A135696 nn=20;With[{ed=RealDigits[E,10,nn][[1]]},Table[FromDigits[Join[Take[ ed,n], Reverse[Take[ed,n-1]]]],{n,nn}]] (* _Harvey P. Dale_, Sep 10 2012 *)
%Y A135696 Cf. A001113, A002113.
%K A135696 base,nonn
%O A135696 1,1
%A A135696 _Omar E. Pol_, Mar 01 2008, corrected Mar 02 2008
%E A135696 More terms from _Harvey P. Dale_, Sep 10 2012