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%I #16 Oct 19 2017 03:14:44
%S 1,2,5,7,15,22,45,54,109,120,241,253,507,523,1047,1065,2131,2150,4301,
%T 4323,8647,8671,17343,17368,34737,34763,69527,69554,139109,139137,
%U 278275,278304,556609,556640,1113281,1113314,2226629,2226663,4453327
%N a(0)=1, a(1)=2; a(2n) = 2*a(2n-1)+1; a(2n+1) = a(2n) + x, where x is the least number not yet the difference of two terms.
%C Each positive integer can be represented exactly once as the difference of two terms.
%H Paul Erdõs, <a href="http://www.jstor.org/stable/2323102">Problem E3202</a>, American Mathematical Monthly, 94(1987), 372. [_N. Sato_, Oct 14 2008]
%e a(4) = 2*a(3)+1 = 15,
%e a(5) = a(4)+7 = 22 because 7 is not yet a difference.
%K easy,nonn
%O 0,2
%A Holger Stephan (stephan(AT)wias-berlin.de), Nov 04 2005
%E Edited by _Don Reble_, May 16 2006
%E Definition corrected by _Guy P. Srinivasan_, Dec 11 2006