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A097285 Contains exactly once every pair (i,j) of distinct positive integers. 7
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, 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, 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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

FORMULA

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.

MAPLE

A097285:= proc(n) local k, j;

   k:= floor(sqrt(n-3/4)-1/2);

   j:= floor((n-k^2-k)/2);

   if n::odd then j+1 else k+2 fi

end proc;

seq(A097285(n), n=1..100); # Robert Israel, May 08 2014

MATHEMATICA

S = {1, 2}; Do[S = Join[S, Riffle[Range[n-1], n], {n}], {n, 3, 12}];

S (* Jean-Fran├žois Alcover, Apr 11 2019 *)

CROSSREFS

Cf. A097286.

Sequence in context: A108663 A307314 A057940 * A057432 A302295 A215467

Adjacent sequences:  A097282 A097283 A097284 * A097286 A097287 A097288

KEYWORD

nonn

AUTHOR

Clark Kimberling, Aug 05 2004

STATUS

approved

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Last modified September 27 22:01 EDT 2022. Contains 357063 sequences. (Running on oeis4.)