A188400 - OEIS

%I #10 Apr 07 2020 14:55:38

%S 1,76,2578,44288,478711,3710272,22393101,111200600,472211360,

%T 1763603560,5916521021,18121655192,51328536740,135834620472,

%U 338676787932,801091475448,1808025242415,3912600581712,8152010122276,16411466716600,32022153082291,60720959942432,112158519503545

%N Number of (6*n) X 6 binary arrays with rows in nonincreasing order, n ones in every column and no more than 2 ones in any row.

%C Number of 6 X 6 symmetric matrices with nonnegative integer entries and all row and column sums n. - _Andrew Howroyd_, Apr 07 2020

%H Andrew Howroyd, <a href="/A188400/b188400.txt">Table of n, a(n) for n = 0..50</a>

%e Some solutions for 12X6

%e ..1..0..0..1..0..0....1..0..0..0..1..0....1..0..0..1..0..0....1..1..0..0..0..0

%e ..1..0..0..0..0..0....1..0..0..0..0..0....1..0..0..0..0..0....1..0..1..0..0..0

%e ..0..1..0..0..0..0....0..1..1..0..0..0....0..1..1..0..0..0....0..1..1..0..0..0

%e ..0..1..0..0..0..0....0..1..0..0..0..0....0..1..1..0..0..0....0..0..0..1..0..1

%e ..0..0..1..1..0..0....0..0..1..1..0..0....0..0..0..1..0..0....0..0..0..1..0..1

%e ..0..0..1..0..0..0....0..0..0..1..0..0....0..0..0..0..1..1....0..0..0..0..1..0

%e ..0..0..0..0..1..1....0..0..0..0..1..0....0..0..0..0..1..0....0..0..0..0..1..0

%e ..0..0..0..0..1..1....0..0..0..0..0..1....0..0..0..0..0..1....0..0..0..0..0..0

%e ..0..0..0..0..0..0....0..0..0..0..0..1....0..0..0..0..0..0....0..0..0..0..0..0

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

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

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

%Y Column 6 of A188403.

%K nonn

%O 0,2

%A _R. H. Hardin_, Mar 30 2011

%E a(0)=1 prepended and terms a(17) and beyond from _Andrew Howroyd_, Apr 07 2020