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%I #5 Mar 31 2012 13:20:01
%S 1,2,7,8,19,20,25,26,55,56,61,62,73,74,79,80,163,164,169,170,181,182,
%T 187,188,217,218,223,224,235,236,241,242,487,488,493,494,505,506,511,
%U 512,541,542,547,548,559,560,565,566,649,650,655,656
%N Related to A055246 and A005836. Used for boundaries of open intervals which have to be erased in the Cantor middle third set construction.
%C 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 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 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 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 Cf. A005836, A055246.
%K nonn,easy
%O 1,2
%A _Wolfdieter Lang_, May 23 2000