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A329185
Number of ways to tile a 2 X n grid with dominoes and L-trominoes such that no four tiles meet at a corner.
2
1, 1, 2, 5, 10, 22, 49, 105, 227, 494, 1071, 2322, 5038, 10927, 23699, 51405, 111498, 241837, 524546, 1137742, 2467761, 5352577, 11609747, 25181550, 54618807, 118468250, 256957750, 557341615, 1208874523, 2622050045, 5687229162, 12335605733, 26755941146
OFFSET
0,3
COMMENTS
a(n) <= A052980(n).
FORMULA
a(n) = 2*a(n-1) - a(n-2) + 3*a(n-3) - a(n-4) + 2*a(n-5), with a(0) = a(1) = 1, a(2) = 2, a(3) = 5, and a(4) = 10.
G.f.: (1 - x)*(1 + x^2) / (1 - 2*x + x^2 - 3*x^3 + x^4 - 2*x^5). - Colin Barker, Nov 12 2019
EXAMPLE
For n=3, the five tilings are:
+---+---+---+ +---+---+---+
| | | | | | |
+ + + + + +---+---+
| | | | | | |
+---+---+---+, +---+---+---+,
+---+---+---+ +---+---+---+
| | | | | |
+---+---+ + + +---+ +
| | | | | |
+---+---+---+, +---+---+---+, and
+---+---+---+
| | |
+ +---+ +
| | |
+---+---+---+.
For n=4, the only tiling counted by A052980(4) that is not counted by a(4) is
+---+---+---+---+
| | |
+---+---+---+---+
| | |
+---+---+---+---+.
MATHEMATICA
LinearRecurrence[{2, -1, 3, -1, 2}, {1, 1, 2, 5, 10}, 50] (* Paolo Xausa, Apr 08 2024 *)
PROG
(PARI) Vec((1 - x)*(1 + x^2) / (1 - 2*x + x^2 - 3*x^3 + x^4 - 2*x^5) + O(x^30)) \\ Colin Barker, Nov 12 2019
CROSSREFS
A052980 is the analogous problem without the "four corners" restriction.
Sequence in context: A018109 A341020 A123491 * A232163 A166300 A038149
KEYWORD
nonn,easy
AUTHOR
Peter Kagey, Nov 07 2019
STATUS
approved