%I A135919
%S A135919 4,11,34,133,566,2488,11056,49323,220373,985176,4405203,19699535,
%T A135919 88096982,393978082,1761917118,7879521402,35238270419,157590299379,
%U A135919 704765178272,3151805575994,14095302829230,63036110202947
%N A135919 Chromatic number of stage-n Menger sponge.
%C A135919 a(n) = A000934(A135918(n))
%D A135919 C. Mackeprang & K. Myers, Coloring Graphs on Sponges, Problem 11208, 
               Amer. Math. Monthly 114 (November 2007), solutions p. 842.
%F A135919 floor((7 + sqrt(1 + 48*(21*20^n + 38*8^n - 59)/133))/2)
%e A135919 a(0)=4 because a cube requires at most 4 colors. a(1)=11 because a cube 
               with holes drilled through the faces meeting in the center requires 
               at most 11 colors.
%Y A135919 Cf. A000934, A135918.
%Y A135919 Sequence in context: A149234 A149235 A149236 this_sequence A034755 A034756 
               A029853
%Y A135919 Adjacent sequences: A135916 A135917 A135918 this_sequence A135920 A135921 
               A135922
%K A135919 easy,nonn
%O A135919 0,1
%A A135919 Marc LeBrun (mlb(AT)well.com), Dec 05 2007