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 A109682 #8 Nov 19 2013 20:09:56 %S A109682 2,7,24,80,238,723,2183,5653,19674,59042,177145,531429,1594313, %T A109682 4782955,14348892,43046708,129140146,387420471,1162261451,3486784397, %U A109682 10460353182,31381059590,94143178804,282429536457,847288609421 %N A109682 Numbers missing from A109681. %C A109682 3^(n-1) < a(n) < 3^n. - _Reinhard Zumkeller_, Nov 19 2013 %o A109682 (Haskell) %o A109682 -- import Data.List (delete) %o A109682 a109682 n = a109682_list !! (n-1) %o A109682 a109682_list = compl a109681_list [0..] where %o A109682 compl us'@(u:us) vs'@(v:vs) %o A109682 | u == v = compl us vs %o A109682 | u > 3 * v = v : compl us (delete u vs) %o A109682 | otherwise = compl us (delete u vs') %o A109682 -- _Reinhard Zumkeller_, Nov 19 2013 %Y A109682 Cf. A109681, A109683, also A109684 (ternary equivalents). %K A109682 nonn %O A109682 1,1 %A A109682 _Philippe Deléham_, Aug 08 2005