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 A331491 a(n) is the permanent of a 2n X 2n antisymmetric Toeplitz matrix M(2n) whose first row consists of a single zero followed by successive positive integers repeated (A004526). 2
 1, -1, 8, -965, 301864, -276973609, 529706205072, -1976989515848629, 12817424808315680000, -136266429300554940901097, 2240244443768853657066332152, -54675928167021488863788002983045, 1910142516402733768189592370043464696, -92787876901046051283841308281722409846473 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Conjecture: for n > 0, det(M(2n)) = n^2 = A000290(n) with det(M(0)) = 1. LINKS Vaclav Kotesovec, Table of n, a(n) for n = 0..18 Wikipedia, Skew-symmetric matrix Wikipedia, Toeplitz Matrix EXAMPLE For n = 2 the matrix M(4) is    0  1  1  2   -1  0  1  1   -1 -1  0  1   -2 -1 -1  0 with permanent a(2) = 8. MATHEMATICA nmax:=13; k[i_]:=Floor[i/2]; a[n_]:=If[n==0, 1, Permanent[ToeplitzMatrix[-Array[k, n], Array[k, n]]]]; Table[a[2n], {n, 0, nmax}] PROG (PARI) tm(n) = {my(m = matrix(n, n, i, j, if (i==1, floor(j/2), if (j==1, -floor(i/2))))); for (i=2, n, for (j=2, n, m[i, j] = m[i-1, j-1]; ); ); m; } a(n) = matpermanent(tm(2*n)); CROSSREFS Cf. A000290, A004526, A083392. Sequence in context: A024111 A231905 A203524 * A300426 A300688 A300611 Adjacent sequences:  A331488 A331489 A331490 * A331492 A331493 A331494 KEYWORD sign AUTHOR Stefano Spezia, Jan 18 2020 STATUS approved

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Last modified November 29 14:50 EST 2021. Contains 349416 sequences. (Running on oeis4.)