A195521 - OEIS

%I #5 Dec 18 2015 18:17:46

%S 1,1,15,1695,2563933,46387885537,10665939121760907,

%T 31749804821289929290261

%N Number of lower triangles of an n X n -7..7 array with all row and column sums zero

%C Column 7 of A195522

%e Some solutions for n=4

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

%e .-1.1......2-2.....-4.4......7-7.....-2.2.....-3.3......3-3......6-6

%e ..3-1-2....1.4-5....3-5.2...-4.0.4...-4.1.3....3-3.0....2.1-3...-2.5-3

%e .-2.0.2.0.-3-2.5.0..1.1-2.0.-3.7-4.0..6-3-3.0..0.0.0.0.-5.2.3.0.-4.1.3.0

%K nonn

%O 1,3

%A _R. H. Hardin_ Sep 20 2011