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 A170951 #3 Nov 04 2013 13:01:50
%S A170951 9,12,13,27,28,30,36,39,40,81,82,84,90,91,108,117,120,121,243,244,246,
%T A170951 252,270,273,324,328,351,360,363,364,729,730,732,738,756,757,810,819,
%U A170951 820,949,972,984,1036,1053,1080,1089,1092,1093,2187
%N A170951 Numbers n with the property that some of the fractions i/n (with gcd(i,n)=1, 0 < i/n < 1) are in the Cantor set and some are not.
%C A170951 Equals A054591 \ {1,3,4,10}.
%C A170951 The natural numbers may be divided into three sets: denominators which force membership in the Cantor set, denominators which deny membership in the Cantor set and denominators which neither force nor deny membership. The first set contains just the numbers 1, 3, 4, 10. The second set is A170944. The third set is the present sequence.
%e A170951 1/9 is in the Cantor set, but 4/9 is not.
%Y A170951 Cf. A005823, A005836, A054591, A121153, A170943, A170944.
%K A170951 nonn,base
%O A170951 1,1
%A A170951 _J. H. Conway_ and _N. J. A. Sloane_, Feb 20 2010