%I
%S 0,0,0,0,1,1,2,3,4,6,7,9,11,13,15,18,20,23,26,29,33,36,40,44,48,52,57,
%T 61,66,71,76,82,87,93,99,105,111,118,124,131,138,145,153,160,168,176,
%U 184,192,201,209,218,227,236,246,255,265,275,285,295,306,316,327,338
%N Minimum number of monochromatic Schur triples over all 2colorings of [n].
%C A Schur triple is an integer triple (x,y,x+y). A 2coloring on [n] = {1,...,n} is a surjective map [n] > {Red, Blue}. A triple (x,y,z) is monochromatic if the set {x,y,z} is mapped to one color. a(n) is exactly the minimum number of monochromatic Schur triples over all possible 2colorings of [n]. The "optimal" coloring for all n (i.e. the coloring that produces the minimum number of monochromatic Schur triples) was shown by Robertson and Zeilberger in 1998 and later with a greedy algorithm by Thanatipanonda in 2009 (see the example for the optimal coloring of [11]). The exact formula for a(n) is computed based on this optimal coloring. One might notice in the literature that there is an additional assumption x<=y. We do not impose this constraint.
%H Elaine Wong, <a href="/A321195/b321195.txt">Table of n, a(n) for n = 1..1000</a>
%H B. Datskovsky, <a href="https://doi.org/10.1016/S01968858(03)000101">On the number of monochromatic Schur triples</a>, Advances in Applied Math, 31 (2003), 193198.
%H A. Robertson and D. Zeilberger, <a href="http://www.combinatorics.org/ojs/index.php/eljc/article/view/v5i1r19">A 2coloring of [1,n] can have n^2/22+O(n) monochromatic Schur triples, but not less!</a>, Electronic Journal of Combinatorics, 5 #R19 (1998).
%H T. Schoen, <a href="https://doi.org/10.1006/eujc.1999.0297">The number of monochromatic Schur Triples</a>, European Journal of Combinatorics, 20 (1999), 855866.
%H T. Thanatipanonda, <a href="http://www.combinatorics.org/ojs/index.php/eljc/article/view/v16i1r14">On the Monochromatic Schur Triples Type Problem</a>, Electronic Journal of Combinatorics, 16(1) #R14 (2009).
%H <a href="/index/Rec#order_13">Index entries for linear recurrences with constant coefficients</a>, signature (2,1,0,0,0,0,0,0,0,0,1,2,1).
%F a(n) = floor((n^2  4*n + 6)/11).
%F G.f.: (x^5 + x^6  x^7  x^10 + x^11  x^12)/ (1 + 2*x  x^2 + x^11  2*x^12 + x^13).
%F a(n) = 2*a(n1)  a(n2) + a(n11)  2*a(n12) + a(n13) for n > 13.  _Colin Barker_, Dec 18 2018
%e On the interval [11], the optimal coloring is R,R,R,R,B,B,B,B,B,B,R, which produces a minimum 7 monochromatic triples (x,y,x+y): (1,1,2), (1,2,3), (2,1,3), (1,3,4), (2,2,4), (3,1,4), (5,5,10).
%p seq(floor((n^24*n+6)/11), n=1..1000);
%t Table[Floor[(n^24n+6)/11], {n,1000}]
%o (GAP) List([1..100],n>Int((n^24*n+6)/11)); # _Muniru A Asiru_, Dec 19 2018
%K nonn
%O 1,7
%A _Elaine Wong_, Dec 18 2018
