OFFSET
0,3
COMMENTS
The shapes of the tiles are:
._.
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._. | |_. | |_._. | |_._._.
|_| |___| |_____| |_______| .
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..1000
Wikipedia, Polyomino
Index entries for linear recurrences with constant coefficients, signature (1,5,9,17,13,5,-2,-2).
FORMULA
G.f.: -(x+1)*(x^3+x-1)/((2*x^2+1)*(x^6+x^5-3*x^4-7*x^3-7*x^2-x+1)).
MATHEMATICA
LinearRecurrence[{1, 5, 9, 17, 13, 5, -2, -2}, {1, 1, 5, 18, 68, 233, 838, 2989}, 30] (* Harvey P. Dale, May 02 2022 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Alois P. Heinz, Dec 12 2018
STATUS
approved