A195515 Number of lower triangles of an n X n -1..1 array with all row and column sums zero.

1, 1, 3, 15, 199, 6247, 505623, 105997283, 58923059879, 87882127554983, 355824020816195749, 3945677945542866439849, 120747614641791880577007593, 10263027079252827219477164325361, 2436143827877272419846561427146618539, 1622665432590314350761059585434700996826279

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