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A097285 Contains exactly once every pair (i,j) of distinct positive integers.

%I A097285 #9 Apr 11 2019 11:45:40
%S A097285 1,2,1,3,2,3,1,4,2,4,3,4,1,5,2,5,3,5,4,5,1,6,2,6,3,6,4,6,5,6,1,7,2,7,
%T A097285 3,7,4,7,5,7,6,7,1,8,2,8,3,8,4,8,5,8,6,8,7,8,1,9,2,9,3,9,4,9,5,9,6,9,
%U A097285 7,9,8,9,1,10,2,10,3,10,4,10,5,10,6,10,7,10,8,10,9,10,1,11,2,11,3,11,4,11,5
%N A097285 Contains exactly once every pair (i,j) of distinct positive integers.
%H A097285 Robert Israel, <a href="/A097285/b097285.txt">Table of n, a(n) for n = 1..10000</a>
%F A097285 Juxtapose segments: 1 2, then 1 3 2 3, then 1 4 2 4 3 4. General segment is 1 n 2 n ... n-1 n, followed by 1, so that clearly, every i<j and every i>j is uniquely present.
%p A097285 A097285:= proc(n) local k,j;
%p A097285    k:= floor(sqrt(n-3/4)-1/2);
%p A097285    j:= floor((n-k^2-k)/2);
%p A097285    if n::odd then j+1 else k+2 fi
%p A097285 end proc;
%p A097285 seq(A097285(n),n=1..100); # _Robert Israel_, May 08 2014
%t A097285 S = {1, 2}; Do[S = Join[S, Riffle[Range[n-1], n], {n}], {n, 3, 12}];
%t A097285 S (* _Jean-François Alcover_, Apr 11 2019 *)
%Y A097285 Cf. A097286.
%K A097285 nonn
%O A097285 1,2
%A A097285 _Clark Kimberling_, Aug 05 2004