A195515 - OEIS

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

(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