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 A037455 #12 Aug 03 2014 14:27:16
%S A037455 0,1,2,7,8,9,14,15,16,49,50,51,56,57,58,63,64,65,98,99,100,105,106,
%T A037455 107,112,113,114,343,344,345,350,351,352,357,358,359,392,393,394,399,
%U A037455 400,401,406,407,408,441,442,443,448,449,450,455,456,457,686,687
%N A037455 a(n)=Sum{d(i)*7^i: i=0,1,...,m}, where Sum{d(i)*3^i: i=0,1,...,m} is the base 3 representation of n.
%H A037455 Clark Kimberling, <a href="/A037455/b037455.txt">Table of n, a(n) for n = 0..1000</a>
%t A037455 Table[FromDigits[RealDigits[n, 3], 7], {n, 0, 100}]
%t A037455 (* _Clark Kimberling_, Aug 13 2012 *)
%K A037455 nonn,base
%O A037455 0,3
%A A037455 _Clark Kimberling_
%E A037455 Changed offset to 0, Clark Kimberling, Aug 13 2012.