A359885 Number of 3-dimensional tilings of a 2 X 2 X 3n box using trominos (three 1 X 1 X 1 cubes).
1, 44, 2512, 145088, 8383744, 484453376, 27994083328, 1617634967552, 93474855387136, 5401434047381504, 312121261353336832, 18035892123135377408, 1042202005934895529984, 60223526164332403490816, 3480009713100277581611008, 201091971436982107249836032
Offset: 0
Examples
a(1)=44. t1,t2,t3 is a tromino standing on 1,2,3 cubes respectively. 1) Two t2-tiles generate a C-profile or a D-profile in 4 ways each. C,D-profile: 4,2 rotation images, D-profile: 2 ways for each image. C-profile D-profiles . ___ ___ ___ . /__ /| ___ /__ /| ___ /__ /| . /__ /| |___ /__ /| | | /__ /| | | .| | |/__ /| | | |___| | | | |___| | .| |/__ /| | | |/__ /| | | |/__ / | .| | |/ | | |/ | | | / .|_______|/ |_______|/ |___|___|/ 2) t1+t3 generates a C-profile in 4*2=8 ways. . ___ . / /| ______ . /__ / | _______ /_____ /| _______ .| | / /__ /| | | | /__ /| .| | | | /__ / | or | __|/ | /__ / | .| | | |_| | / | | | |_| | / .|___|/ |___|/ |___|/ |___|/ 1,2) There are 12 ways to generate a C-profile. The connection of two C-profiles is a 2 X 2 X 3 cuboid. Starting with a C-profile, there are 4*3*3=36 ways to generate this cuboid. 3) There are 4*2=8 ways to generate the cuboid by starting with a D-profile. Therefore, a(1)=36+8=44. . ___ . / /| ___ ___ . /__ / | ___ /__ /| / /| .| | | /__ /| | | /__ / | .|___|/| | | | |___| | | | / . |___|/ | |/__ /| | | | | or . | | |/ | | | . |_______|/ |___|/ . _______ . /______ /| ___ .| | | ___ /__ /| _______ .| ___|/ /__ /| | | /______ /| .| | | | | |___| | | | | .|___|/ | |/__ /| | |___ | | . | | |/ | | | . |_______|/ |___|/
Links
- Paolo Xausa, Table of n, a(n) for n = 0..500
- Index entries for linear recurrences with constant coefficients, signature (60,-128).
Programs
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Mathematica
LinearRecurrence[{60, -128}, {1, 44}, 20] (* Paolo Xausa, Jun 24 2024 *)
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Maxima
/* See A359884. */
Formula
G.f.: (1 - 16*x) / (1 - 60*x + 128*x^2).
a(n) = 44*a(n-1) + 6*e(n-1) where e(n) = 96*a(n-1) + 16*e(n-1) with a(n),e(n) <= 0 for n < =0 except for a(0)=1.
a(n) = 60*a(n-1) - 128*a(n-2) for n >= 2.
E.g.f.: exp(30*x)*cosh(2*sqrt(193)*x) + 7*exp(30*x)*sinh(2*sqrt(193)*x)/sqrt(193). - Stefano Spezia, Jan 21 2023
Comments