Number of 2n X 2n symmetric matrices whose first row is 1..2n and whose rows and columns are all permutations of 1..2n.

A035483

Number of 2n X 2n symmetric matrices whose first row is 1..2n and whose rows and columns are all permutations of 1..2n.

Terms

    a(0) =1a(1) =1a(2) =4a(3) =456a(4) =10936320

External references