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Weisstein's conjecture states that, for each positive integer 
,
the number of 
(0,1)-matrices all of whose eigenvalues
are positive real numbers
equals the number of labeled acyclic digraphs
on 
vertices. Eric Weisstein formulated the conjecture on
July 10, 2003 after computing the counts 1, 3, 25, 543, and 29281 for 
, 2, ..., 5 (OEIS A003024;
McKay et al. 2004, pp. 1-2).
This result was subsequently proved by McKay et al. (2003, 2004).
-Matrices." 28 Oct 2003. https://arxiv.org/abs/math/0310423.McKay,
B. D.; Oggier, F. E.; Royle, G. F.; Sloane, N. J. A.; Wanless,
I. M.; and Wilf, H. S. "Acyclic Digraphs and Eigenvalues of 
-Matrices." J. Integer Sequences 7,
Article 04.3.3, 1-5, 2004. https://cs.uwaterloo.ca/journals/JIS/VOL7/Sloane/sloane15.html.Sloane,
N. J. A. Sequence A003024/M3113
in "The On-Line Encyclopedia of Integer Sequences."Weisstein, Eric W. "Weisstein's Conjecture." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/WeissteinsConjecture.html
