A278815 Number of tilings of a 2 X n grid with monomers, dimers, and trimers.

1, 2, 7, 29, 109, 416, 1596, 6105, 23362, 89415, 342193, 1309593, 5011920, 19180976, 73406985, 280933906, 1075154535, 4114694797, 15747237101, 60265824784, 230641706484, 882682631025, 3378090801226, 12928199853783, 49477163668857, 189352713633433

Offset: 0

Author

Kathryn Haymaker, Nov 28 2016

Keywords

• nonn
• easy

Comments

The first three terms are the same as A030186 because there are only monomers and dimers in boards with n<3.

Links

• Alois P. Heinz, Table of n, a(n) for n = 0..1000
• Kathryn Haymaker and Sara Robertson, Counting Colorful Tilings of Rectangular Arrays, Journal of Integer Sequences, Vol. 20 (2017), Article 17.5.8, Corollary 2.
• Index entries for linear recurrences with constant coefficients, signature (3,2,5,-2,0,-1).

Crossrefs

Cf. A030186, A052961, A129682, A219866.

Programs

GAP

a:=[1,2,7,29,109,416];; for n in [7..30] do a[n]:=3*a[n-1]+2*a[n-2] +5*a[n-3]-2*a[n-4]-a[n-6]; od; a; # G. C. Greubel, Oct 28 2019

Magma

R:=PowerSeriesRing(Integers(), 30); Coefficients(R!( (1-x-x^2-x^3)/(1-3*x-2*x^2-5*x^3+2*x^4+x^6) )); // G. C. Greubel, Oct 28 2019

Maple

seq(coeff(series((1-x-x^2-x^3)/(1-3*x-2*x^2-5*x^3+2*x^4+x^6), x, n+1), x, n), n = 0..30); # G. C. Greubel, Oct 28 2019

Mathematica

LinearRecurrence[{3,2,5,-2,0,-1}, {1,2,7,29,109,416}, 30] (* G. C. Greubel, Oct 28 2019 *)

PARI

my(x='x+O('x^30)); Vec((1-x-x^2-x^3)/(1-3*x-2*x^2-5*x^3+ 2*x^4 +x^6)) \\ G. C. Greubel, Oct 28 2019

Sage

def A278815_list(prec):
    P. = PowerSeriesRing(ZZ, prec)
    return P( (1-x-x^2-x^3)/(1-3*x-2*x^2-5*x^3+2*x^4+x^6) ).list()
A278815_list(30) # G. C. Greubel, Oct 28 2019

Formula

a(n) = 3*a(n-1) + 2*a(n-2) + 5*a(n-3) - 2*a(n-4) - a(n-6).

G.f.: (1 - x - x^2 - x^3)/(1 - 3*x - 2*x^2 - 5*x^3 + 2*x^4 + x^6).