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A335606
The number of fixed n-ominoes with a convex hull of width 3.
1
1, 8, 31, 95, 269, 721, 1866, 4728, 11804, 29162, 71502, 174342, 423341, 1024786, 2474934, 5966625, 14365256, 34550674, 83035396, 199440433, 478814076, 1149133511, 2757142136, 6613933242, 15863281135, 38042981575, 91225540813, 218739876078, 524464594304, 1257437814143, 3014693395137
OFFSET
3,2
COMMENTS
Obtained from Zeilberger's tables by subtracting the numbers of width <= 3 and of width <= 2.
FORMULA
a(n) = A308359(n,3).
G.f.: -x^3*(1+x) *(x^10 -x^9 -3*x^8 +2*x^7 -x^6 -2*x^5 +7*x^4 -3*x^3 -5*x^2 +2*x +1) / ( (x-1) *(x^3 +x^2 +x -1) *(x^10 -3*x^9 -x^8 +2*x^6 +x^4 -4*x^3 +3*x -1) ).
a(n)= 5*a(n-1) -6*a(n-2) -4*a(n-3) +8*a(n-4) +a(n-5) +2*a(n-6) -8*a(n-7) -a(n-9) +9*a(n-10) -2*a(n-11) -a(n-12) -3*a(n-13) +a(n-14).
EXAMPLE
a(3)=1 counts 1 3-omino of shape 1x3.
a(4)=8 counts 8 4-ominoes of shape 2x3.
a(5)=31 counts 6 5-ominoes of shape 2x3 and 25 5-ominoes of shape 3x3.
a(6)=95 counts 1 6-omino of shape 2x3, 44 6-ominoes of shape 3x3 and 50 6-ominoes of shape 4x3.
MATHEMATICA
LinearRecurrence[{5, -6, -4, 8, 1, 2, -8, 0, -1, 9, -2, -1, -3, 1}, {1, 8, 31, 95, 269, 721, 1866, 4728, 11804, 29162, 71502, 174342, 423341, 1024786, 2474934}, 31] (* Georg Fischer, Jan 16 2021 *)
CROSSREFS
Cf. A308359, A027053 (width 2).
Sequence in context: A319906 A212064 A213764 * A320416 A289613 A055845
KEYWORD
nonn,easy
AUTHOR
R. J. Mathar, Jun 15 2020
STATUS
approved