A057629 Number of alternating sign 2n X 2n matrices invariant under flips in both diagonals.

2, 8, 52, 568, 10436, 323144, 16866856, 1484714416, 220426128584

Offset: 1

Author

N. J. A. Sloane, Oct 10 2000

Keywords

• nonn
• more
• nice

Links

• D. P. Robbins, Symmetry classes of alternating sign matrices, arXiv:math/0008045 [math.CO], 2000.

Crossrefs

Even numbered terms of A005162.

Cf. A059475.

Formula

a(n) = A005162(2*n).

Extensions

a(8)-a(9) from A005162(2*n) by Jinyuan Wang, Mar 03 2020