0,3

There are 5 nonisomorphic 4 X 4 matrices with row and column sums 2:

[0 0 0 2] [0 0 0 2] [0 0 0 2] [0 0 1 1] [0 0 1 1]

[0 0 2 0] [0 0 2 0] [0 1 1 0] [0 0 1 1] [0 1 0 1]

[0 2 0 0] [1 1 0 0] [1 0 1 0] [1 1 0 0] [1 0 1 0]

[2 0 0 0] [1 1 0 0] [1 1 0 0] [1 1 0 0] [1 1 0 0]

Cf. A001496, A052281, A052282.

Sequence in context: A082189 A129795 A052644 this_sequence A006078 A046612 A009425

Adjacent sequences: A052277 A052278 A052279 this_sequence A052281 A052282 A052283

more,nonn

Vladeta Jovovic (vladeta(AT)Eunet.yu), Feb 06 2000