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 A055247 #5 Mar 31 2012 13:20:01 %S A055247 1,2,7,8,19,20,25,26,55,56,61,62,73,74,79,80,163,164,169,170,181,182, %T A055247 187,188,217,218,223,224,235,236,241,242,487,488,493,494,505,506,511, %U A055247 512,541,542,547,548,559,560,565,566,649,650,655,656 %N A055247 Related to A055246 and A005836. Used for boundaries of open intervals which have to be erased in the Cantor middle third set construction. %C A055247 At step number k >= 1 the 2^(k-1) open intervals which are erased from [0,1] in the Cantor middle third set construction are: I(k,n)=(a(2*n-1)/3^k,a(2*n)/3^k), n=1,.,2^(k-1). %F A055247 a(n)= A055246((n+1)/2) if n odd, a(n)= A055246(n/2)+1 if n even. A055246(n)= 1+6*A005836(n-1), n >= 1. %F A055247 a(1) = 1, a(n) = 3^ceiling( log_2( n ) ) - a( 2^ceiling( log_2( n ) ) + 1 - n ). - Juan Jose Alba Gonzalez (jjalba(AT)gmail.com), May 16 2006 %e A055247 k=1: (1/3, 2/3); k=2: (1/9, 2/9), (7/9, 8/9); k=3: (1/27, 2/27), (7/27, 8/27), (19/27, 20/27), (25/27, 26/27); ... %Y A055247 Cf. A005836, A055246. %K A055247 nonn,easy %O A055247 1,2 %A A055247 _Wolfdieter Lang_, May 23 2000