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 A195515 Number of lower triangles of an n X n -1..1 array with all row and column sums zero. 1
 1, 1, 3, 15, 199, 6247, 505623, 105997283, 58923059879, 87882127554983, 355824020816195749, 3945677945542866439849, 120747614641791880577007593, 10263027079252827219477164325361, 2436143827877272419846561427146618539, 1622665432590314350761059585434700996826279 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 LINKS Table of n, a(n) for n=1..16. EXAMPLE Some solutions for 4 X 4: ..0........0........0........0........0........0........0........0 ..1-1.....-1.1......1-1......0.0.....-1.1......0.0.....-1.1......1-1 ..0.0.0....1-1.0....0.0.0....0.0.0....0.0.0....1.0-1....0.0.0...-1.1.0 .-1.1.0.0..0.0.0.0.-1.1.0.0..0.0.0.0..1-1.0.0.-1.0.1.0..1-1.0.0..0.0.0.0 CROSSREFS Column 1 of A195522 and column 2 of A195644. Sequence in context: A068858 A280772 A166359 * A003505 A270354 A120601 Adjacent sequences: A195512 A195513 A195514 * A195516 A195517 A195518 KEYWORD nonn AUTHOR R. H. Hardin, Sep 20 2011 EXTENSIONS a(13)-a(16) from Andrew Howroyd, May 16 2020 STATUS approved

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Last modified June 8 07:54 EDT 2023. Contains 363157 sequences. (Running on oeis4.)