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 A175909 #2 Mar 31 2012 20:01:58
%S A175909 1,1,7,46,29,219,495,1502,368357,27603,120539,1797358,462906349,
%T A175909 32361431,33008607,12857291758,5972138981,750631865,99509722923,
%U A175909 13841055262,31762354574285,1019248986603,8645573738319287
%N A175909 Decimal representation of the binary number formed by the concatenation of digits which are the same in both the left and right binary concatenations of the integers 1 to n.
%t A175909 Module[{l,r,d},l = {}; r = {}; Table[d = IntegerDigits[x, 2]; l = Flatten[{l, d}]; r = Flatten[{d, r}]; FromDigits[ Pick[l, EvenQ[l + r]], 2], {x, 1, DESIRED_NUMBER_OF_TERMS}]]
%Y A175909 Cf. A047778, A098780
%K A175909 base,easy,nonn
%O A175909 1,3
%A A175909 _Dylan Hamilton_, Oct 14 2010