%I A135918
%S A135918 0,5,81,1409,26433,514625,10180161,202704449,4046898753,80880453185,
%T A135918 1617148888641,32339296372289,646756476241473,12934893915194945,
%U A135918 258695993426822721,5173904789519844929,103477975158264022593
%N A135918 Genus of stage-n Menger sponge.
%D A135918 C. Mackeprang & K. Myers, Coloring Graphs on Sponges, Problem 11208, 
               Amer. Math. Monthly 114 (November 2007), solutions p. 842.
%F A135918 (21*20^n + 38*8^n - 59)/133
%e A135918 a(0)=0 because a cube has genus 0. a(1)=5 because a cube with holes drilled 
               through the faces meeting in the center has genus 5.
%Y A135918 Cf. A135919.
%Y A135918 Sequence in context: A144344 A062364 A110257 this_sequence A115032 A009733 
               A009756
%Y A135918 Adjacent sequences: A135915 A135916 A135917 this_sequence A135919 A135920 
               A135921
%K A135918 easy,nonn
%O A135918 0,2
%A A135918 Marc LeBrun (mlb(AT)well.com), Dec 05 2007