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 A272661 Number of distinct characteristic polynomials of n X n matrices with elements {0, 1}. 10
 2, 6, 32, 333, 8927, 758878 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 REFERENCES Robert M. Corless, Bohemian Eigenvalues, Talk Presented at Computational Discovery in Mathematics (ACMES 2), University of Western Ontario, May 12 2016. (Talk based on joint work with Steven E. Thornton, Sonia Gupta, Jonathan Brino-Tarasoff, Venkat Balasubramanian.) LINKS Robert M. Corless, Steven E. Thornton, Sonia Gupta, Jonathan Brino-Tarasoff, Venkat Balasubramanian, Slides from "Bohemian Eigenvalues" talk. Robert Israel, Examples for n=5 PROG (MATLAB) function count = A272661(N)   C = zeros(0, N);   count = 0;   V = zeros(1, N);   L = -floor(N/2) + [0:N-1];   for x = 0:2^(N^2)-1;     r = dec2bin(x+2^(N^2))-'0';     A = reshape(r(2:end), N, N);     rowcounts = sum(A, 2);     colcounts = sum(A, 1);     if ~issorted(rowcounts)|| rowcounts(N) < max(colcounts)       continue     end     for i = 1:N         V(i) = round(det(A - L(i)*eye(N)));     end     if ~ismember(V, C, 'rows')       count = count+1;       C(count, :) = V;     end   end end  % Robert Israel, Aug 18 2016 CROSSREFS Six classes of matrices mentioned in Rob Corless's talk: A272658, A272659, A272660, A272661, A272662, A272663. Sequence in context: A005736 A123903 A172401 * A005742 A055612 A236691 Adjacent sequences:  A272658 A272659 A272660 * A272662 A272663 A272664 KEYWORD nonn,more AUTHOR N. J. A. Sloane, May 15 2016 EXTENSIONS a(5) from Robert Israel, Aug 18 2016 a(6) from Steven E. Thornton, Mar 09 2019 STATUS approved

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Last modified January 19 17:59 EST 2020. Contains 331051 sequences. (Running on oeis4.)