cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

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A004003 Number of domino tilings (or dimer coverings) of a 2n X 2n square.

Original entry on oeis.org

1, 2, 36, 6728, 12988816, 258584046368, 53060477521960000, 112202208776036178000000, 2444888770250892795802079170816, 548943583215388338077567813208427340288, 1269984011256235834242602753102293934298576249856
Offset: 0

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Author

Keywords

Comments

A099390 is the main entry for domino tilings (or dimer tilings) of a rectangle.
The numbers of domino tilings in A006253, A004003, A006125 give the number of perfect matchings in the relevant graphs. There are results of Jockusch and Ciucu that if a planar graph has a rotational symmetry then the number of perfect matchings is a square or twice a square - this applies to these 3 sequences. - Dan Fux (dan.fux(AT)OpenGaia.com or danfux(AT)OpenGaia.com), Apr 12 2001
Christine Bessenrodt points out that Pachter (1997) shows that a(n) is divisible by 2^n (cf. A065072).
a(n) is the number of different ways to cover a 2n X 2n lattice with 2n^2 dominoes. John and Sachs show that a(n) = 2^n*B(n)^2, where B(n) == n+1 (mod 32) when n is even and B(n) == (-1)^((n-1)/2)*n (mod 32) when n is odd. - Yong Kong (ykong(AT)curagen.com), May 07 2000

Examples

			The 36 solutions for the 4 X 4 board, from Neven Juric, May 14 2008:
A01 = {(1,2), (3,4), (5,6), (7,8), (9,10), (11,12), (13,14), (15,16)}
A02 = {(1,2), (3,4), (5,6), (7,11), (9,10), (8,12), (13,14), (15,16)}
A03 = {(1,2), (3,4), (5,9), (6,7), (10,11), (8,12), (13,14), (15,16)}
A04 = {(1,2), (3,4), (5,9), (6,10), (7,8), (11,12), (13,14), (15,16)}
A05 = {(1,2), (3,4), (5,9), (6,10), (7,11), (8,12), (13,14), (15,16)}
A06 = {(1,2), (3,4), (5,6), (7,8), (9,10), (13,14), (11,15), (12,16)}
A07 = {(1,2), (3,4), (5,9), (6,10), (7,8), (11,15), (13,14), (12,16)}
A08 = {(1,2), (3,4), (5,6), (7,8), (9,13), (10,14), (11,12), (15,16)}
A09 = {(1,2), (3,4), (5,6), (7,11), (8,12), (9,13), (10,14), (15,16)}
A10 = {(1,2), (3,4), (5,6), (7,8), (9,13), (10,11), (14,15), (12,16)}
A11 = {(1,2), (3,4), (5,6), (7,8), (9,13), (10,14), (11,15), (12,16)}
A12 = {(1,2), (5,6), (3,7), (4,8), (9,10), (11,12), (13,14), (15,16)}
A13 = {(1,2), (3,7), (4,8), (5,9), (6,10), (11,12), (13,14), (15,16)}
A14 = {(1,2), (5,6), (3,7), (4,8), (9,10), (13,14), (11,15), (12,16)}
A15 = {(1,2), (3,7), (4,8), (6,10), (5,9), (11,15), (12,16), (13,14)}
A16 = {(1,2), (3,7), (4,8), (5,6), (9,13), (10,14), (11,12), (15,16)}
A17 = {(1,2), (3,7), (4,8), (5,6), (9,13), (10,11), (14,15), (12,16)}
A18 = {(1,2), (5,6), (3,7), (4,8), (9,13), (10,14), (11,15), (12,16)}
A19 = {(1,5), (2,6), (3,4), (7,8), (9,10), (11,12), (13,14), (15,16)}
A20 = {(1,5), (2,6), (3,4), (7,11), (8,12), (9,10), (13,14), (15,16)}
A21 = {(1,5), (3,4), (2,6), (9,10), (7,8), (11,15), (13,14), (12,16)}
A22 = {(1,5), (2,6), (3,4), (7,8), (9,13), (10,14), (11,12), (15,16)}
A23 = {(1,5), (2,6), (3,4), (7,11), (8,12), (9,13), (10,14), (15,16)}
A24 = {(1,5), (2,6), (3,4), (7,8), (9,13), (10,11), (14,15), (12,16)}
A25 = {(1,5), (2,6), (3,4), (7,8), (9,13), (10,14), (11,15), (12,16)}
A26 = {(1,5), (2,3), (6,7), (4,8), (9,10), (11,12), (13,14), (15,16)}
A27 = {(1,5), (2,6), (3,7), (4,8), (9,10), (11,12), (13,14), (15,16)}
A28 = {(1,5), (2,3), (6,7), (4,8), (9,10), (11,15), (13,14), (12,16)}
A29 = {(1,5), (2,6), (3,7), (4,8), (9,10), (13,14), (11,15), (12,16)}
A30 = {(1,5), (2,3), (6,7), (4,8), (9,13), (10,14), (11,12), (15,16)}
A31 = {(1,5), (2,6), (3,7), (4,8), (9,13), (10,14), (11,12), (15,16)}
A32 = {(1,5), (2,6), (3,7), (4,8), (9,13), (10,14), (11,15), (12,16)}
A33 = {(1,5), (2,6), (3,7), (4,8), (9,13), (10,11), (14,15), (12,16)}
A34 = {(1,5), (2,3), (4,8), (6,10), (7,11), (9,13), (14,15), (12,16)}
A35 = {(1,5), (2,3), (6,7), (4,8), (9,13), (10,14), (11,15), (12,16)}
A36 = {(1,5), (2,3), (6,7), (4,8), (9,13), (10,11), (14,15), (12,16)}
		

References

  • Miklos Bona, editor, Handbook of Enumerative Combinatorics, CRC Press, 2015, page 569.
  • S. R. Finch, Mathematical Constants, Cambridge, 2003, pp. 406-412.
  • N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
  • Darko Veljan, Kombinatorika s teorijom grafova (Croatian) (Combinatorics with Graph Theory) mentions the value 12988816 = 2^4*901^2 for the 8 X 8 case on page 4.

Crossrefs

Main diagonal of array A099390 or A187596.

Programs

  • Maple
    f := n->2^(2*n^2)*product(product(cos(i*Pi/(2*n+1))^2+cos(j*Pi/(2*n+1))^2,j=1..n),i=1..n); for k from 0 to 12 do round(evalf(f(k),300)) od;
  • Mathematica
    a[n_] := Round[ N[ Product[ 2*Cos[(2i*Pi)/(2n+1)] + 2*Cos[(2j*Pi)/(2n+1)] + 4,  {i, 1, n}, {j, 1, n}], 300] ]; Table[a[n], {n, 0, 12}] (* Jean-François Alcover, Jan 04 2012, after Maple *)
    Table[Sqrt[Resultant[ChebyshevU[2*n, x/2], ChebyshevU[2*n, I*x/2], x]], {n, 0, 12}] (* Vaclav Kotesovec, Dec 30 2020 *)
  • PARI
    {a(n) = sqrtint(polresultant(polchebyshev(2*n, 2, x/2), polchebyshev(2*n, 2, I*x/2)))} \\ Seiichi Manyama, Apr 13 2020
    
  • Python
    from math import isqrt
    from sympy.abc import x
    from sympy import I, resultant, chebyshevu
    def A004003(n): return isqrt(resultant(chebyshevu(n<<1,x/2),chebyshevu(n<<1,I*x/2))) if n else 1 # Chai Wah Wu, Nov 07 2023

Formula

a(n) = A099390(2n,2n).
a(n) = Product_{j=1..n} Product_{k=1..n} (4*cos(j*Pi/(2*n+1))^2 + 4*cos(k*Pi/(2*n+1))^2). - N. J. A. Sloane, Mar 16 2015
a(n) = 2^n * A065072(n)^2. - Alois P. Heinz, Nov 22 2018
a(n)^2 = Resultant(U(2*n,x/2), U(2*n,i*x/2)), where U(n,x) is a Chebyshev polynomial of the second kind and i = sqrt(-1). - Seiichi Manyama, Apr 13 2020
a(n) ~ 2 * (sqrt(2)-1)^(2*n+1) * exp(G*(2*n+1)^2/Pi), where G is Catalan's constant A006752. - Vaclav Kotesovec, Dec 30 2020

Extensions

Corrected and extended by David Radcliffe

A334396 Number of fault-free tilings of a 3 X n rectangle with squares and dominoes.

Original entry on oeis.org

0, 0, 2, 2, 10, 16, 52, 104, 286, 634, 1622, 3768, 9336, 22152, 54106, 129610, 314546, 756728, 1831196, 4413952, 10667462, 25735346, 62160046, 150020016, 362257392, 874442064, 2111291570, 5096782418, 12305249242, 29706645280, 71719568260
Offset: 1

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Comments

A fault-free tiling has no horizontal or vertical faults (that is to say, the tiling does not split along any interior horizontal or vertical line).

Examples

			a(4) = 2 because these are the only fault-free tilings of the 3 X 4 rectangle with squares and dominoes:
._ _ _ _     _ _ _ _
|_ _|_| |   | |_|_ _|
| |_ _|_|   |_|_ _| |
|_|_|_ _|   |_ _|_|_|
		

Crossrefs

Programs

  • Magma
    [n le 4 select 2*Floor((n-1)/2) else Self(n-1) +4*Self(n-2) -Self(n-3) -Self(n-4): n in [1..40]]; // G. C. Greubel, Jan 15 2022
    
  • Mathematica
    a[n_]:= (2/3)*(Fibonacci[n-1, 2] - (-1)^n*Fibonacci[n-1]);
    Table[a[n], {n, 40}] (* G. C. Greubel, Jan 15 2022 *)
  • PARI
    concat([0,0] , Vec(2*x^3/((1+x-x^2)*(1-2*x-x^2)) + O(x^30))) \\ Colin Barker, Aug 06 2020
    
  • Sage
    [(2/3)*(lucas_number1(n-1,2,-1) - (-1)^n*lucas_number1(n-1,1,-1)) for n in (1..40)] # G. C. Greubel, Jan 15 2022

Formula

a(n) = a(n-1) + 4*a(n-2) - a(n-3) - a(n-4) for n >= 5.
a(n) = 2*A112577(n-2) for n >= 2.
G.f.: 2*x^3 / ((1 + x - x^2)*(1 - 2*x - x^2)). - Colin Barker, Aug 06 2020
Showing 1-2 of 2 results.