The number of ways to cover an m × × n rectangle with m n 2 dominoes, calculated independently by Temperley & Fisher (1961) and Kasteleyn (1961), is given by ∏ ∏ j = 1 ⌈ ⌈ m 2 ⌉ ⌉ ∏ ∏ k = 1 ⌈ ⌈ n 2 ⌉ ⌉ ( 4 cos 2 ⁡ ⁡ π π j m + 1 + 4 cos 2 ⁡ ⁡ π π k n + 1 ) . (sequence A099390 in the OEIS)