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 A211864 #8 Feb 11 2013 14:43:53 %S A211864 1,3,9,11,17,19,41,43,81,131,169,219,241,419,681,651,849,1203,2441, %T A211864 1867,4369,3027,5625,12475,15457,26403,26553,48795,54561,99667,80345, %U A211864 158731,221313,332467,460857,375451,569345,987267,1181145,1594971,1924001,4458531 %N A211864 Powers of three read in base 2. %e A211864 a(3)=11 because 3^3=27_10 but in base 2 it is interpreted as 2*2^1+7*2^0=4+7=11. That is to say, digits larger than the base are carried. %t A211864 f[n_] := FromDigits[ IntegerDigits[3^n], 2]; Array[f, 42, 0] %Y A211864 Cf. A004656. %K A211864 nonn,base,easy %O A211864 0,2 %A A211864 _Robert G. Wilson v_, Feb 10 2013