A195885 - OEIS

%I #6 Dec 18 2015 18:17:46

%S 1,1,3,15,83,591,5281,56249,704129,10236185,170423795,3211956071,

%T 67925755107,1599937402631

%N Number of lower triangles of an n X n integer array with all row and column sums zero and all row and column sums of squares <=2

%C Column 1 of A195892

%e Some solutions for n=4

%e ..0........0........0........0........0........0........0........0

%e ..0.0.....-1.1.....-1.1......0.0.....-1.1......0.0......1-1......1-1

%e ..0.0.0....0.0.0....0.0.0...-1.1.0....0.0.0....0-1.1...-1.1.0....0.0.0

%e ..0.0.0.0..1-1.0.0..1-1.0.0..1-1.0.0..1-1.0.0..0.1-1.0..0.0.0.0.-1.1.0.0

%K nonn

%O 1,3

%A _R. H. Hardin_ Sep 24 2011