OFFSET
1,2
LINKS
B. D. McKay, F. E. Oggier, G. F. Royle, N. J. A. Sloane, I. M. Wanless and H. S. Wilf, Acyclic digraphs and eigenvalues of (0,1)-matrices, J. Integer Sequences, 7 (2004), #04.3.3.
B. D. McKay, F. E. Oggier, G. F. Royle, N. J. A. Sloane, I. M. Wanless and H. S. Wilf, Acyclic digraphs and eigenvalues of (0,1)-matrices, arXiv:math/0310423 [math.CO], 2003.
Eric Weisstein's World of Mathematics, Positive Definite Matrix
MATHEMATICA
a[n_] := Module[{M, iter, cnt = 0}, M = Table[a[i, j], {i, 1, n}, {j, 1, n}]; iter = Thread[{Flatten[M], -1, 1}]; Do[If[AllTrue[Eigenvalues[M], If[Im[#] != 0, False, Positive[#]]&], cnt++], Evaluate[Sequence @@ iter]]; cnt];
Do[Print[n, " ", a[n]], {n, 1, 3}] (* Jean-François Alcover, Dec 09 2018 *)
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Eric W. Weisstein, Jul 02 2003
EXTENSIONS
Offset corrected by Max Alekseyev, Oct 18 2008
STATUS
approved