Enumeration of Alternating Sign Matrices of Even Size (Quasi-)Invariant under a Quarter-Turn Rotation

@article{Aval2010EnumerationOA,
  title={Enumeration of Alternating Sign Matrices of Even Size (Quasi-)Invariant under a Quarter-Turn Rotation},
  author={Jean-Christophe Aval and Philippe Duchon},
  journal={Electr. J. Comb.},
  year={2010},
  volume={17}
}
The aim of this work is to enumerate alternating sign matrices (ASM) that are quasi-invariant under a quarter-turn. The enumeration formula (conjectured by Duchon) involves, as a product of three terms, the number of unrestricted ASM’s and the number of half-turn symmetric ASM’s.