A181344 Number of n X n matrices over {0,1} with rows and columns summing to 3, rows and columns sorted (>=) by value.

0, 0, 1, 1, 5, 25, 161, 1112, 8787, 76156, 728699, 7609065, 86162795, 1050755884, 13728407061, 191309852944

Offset: 1

Author

Michael Steyer (m.steyer(AT)osram.de), Oct 14 2010

Keywords

• hard
• more
• nonn

Examples

			n=4: {1110,1101,1011,0111} is the only matrix where each row (column) - read as a binary number - is equal to or larger than the previous one, so a(4)=1.
		

Links

• Bert Dobbelaere, Illustration of initial terms

Crossrefs

Cf. A000512, A001501, A181345.

Extensions

a(10)-a(16) from Bert Dobbelaere, Feb 23 2020