A352258 - OEIS

%I #10 Mar 17 2022 09:24:45

%S 2,7,42,399,5614,112221,3102020,116076057,5774524092,376068483351,

%T 31643635513816,3401292647423655,462391295351625128,

%U 78801283167350942685,1775935516860530625139,230933325874558862792569

%N Number of symmetric binary n X n matrices with no 2 X 2 submatrix of all 1s.

%C Equivalently, the number of labeled graphs (loops but not multiple edges allowed) with none of these subgraphs: 4-cycle, edge with a loop on each end, triangle with at least one loop.

%Y Row sums of A350189.

%Y Cf. A345249 (traceless matrices).

%K nonn,hard

%O 1,1

%A _Brendan McKay_, Mar 09 2022