Domino Tiling

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The Fibonacci number F_(n+1) gives the number of ways for 2×1 dominoes to cover a 2×n checkerboard, as illustrated in the diagrams above (Dickau).

DominoTilings

The numbers of domino tilings, also known as dimer coverings, of a 2n×2n square for n=1, 2, ... are given by 2, 36, 6728, 12988816, ... (OEIS A004003). The 36 tilings on the 4×4 square are illustrated above. A formula for these numbers is given by

 A_n=2^(2n^2)product_(i=1)^nproduct_(j=1)^n[cos^2((ipi)/(2n+1))+cos^2((jpi)/(2n+1))].
(1)

Writing

 B_n^2=2^(-n)A_n,
(2)

gives the surprising result

 A_n (mod 32)={n+1 (mod 32)   for n even; (-1)^((n-1)/2)n (mod 32)   for n odd
(3)

(John and Sachs 2000). For n=1, 2, ..., the first few terms are 1, 3, 29, 5, 5, 7, 25, 9, 9, 11, 21, ... (OEIS A143234).

Writing

B=lim_(n->infty)(lnA_n)/((2n)^2)
(4)
=1/(16pi^2)int_(-pi)^piint_(-pi)^piln[4+2costheta+2cosphi]dthetadphi
(5)
=K/pi
(6)
=0.291560904...
(7)

(OEIS A143233), where K is Catalan's constant.

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