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A136290 a(0)=1, a(1)=3, a(2)=9, a(3)=12, a(4)=15; thereafter a(n) = a(n-1) + a(n-3) - a(n-4). 2
1, 3, 9, 12, 15, 21, 24, 27, 33, 36, 39, 45, 48, 51, 57, 60, 63, 69, 72, 75, 81, 84, 87, 93, 96, 99, 105, 108, 111, 117, 120, 123, 129, 132, 135, 141, 144, 147, 153, 156, 159, 165, 168, 171, 177, 180, 183, 189, 192, 195, 201, 204, 207, 213, 216, 219, 225, 228, 231, 237 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,2
COMMENTS
This is the coordination sequence for Marjorie Rice's tiling of the plane shown in Fig. 15 of Schattschneider (1981), with respect to the central vertex. The Schattschneider illustration below shows that the first differences of the coordination sequence are 2, 6, 3, 3, 6, 3, 3, 6, 3, 3, ..., and so the sequence itself satisfies the recurrence in the definition. The tiling has symmetry group D_6 (the dihedral group of order 6).
Continuing from the arrangement of pennies described in A136289, we also wish to place dimes over the holes in the array, where the n-th generation of dimes can be placed only when all three of its supporting pennies are in place already; then a(n-1) is the number of dimes in generation n for >= 1. - Colin Mallows, Apr 13 2008
REFERENCES
Doris Schattschneider, In Praise of Amateurs, pp. 140-166 in D. A. Klarner, editor, The Mathematical Gardner. Prindle, Weber and Schmidt, Boston, 1981.
LINKS
N. J. A. Sloane, Illustration of terms a(0) to a(9) of the coordination sequence for the Rice tiling [Annotated copy of Fig. 15 of Schattschneider (1981)]
FORMULA
G.f.: (1 + 2*x + 6*x^2 + 2*x^3 + x^4)/((1-x)^2*(1+x+x^2)). - Colin Barker, Jul 12 2014
a(n) = [n=0] + 4*n - ChebyshevU(n-1, -1/2). - G. C. Greubel, Apr 13 2021
For n > 0, a(n) = 3*A042965(n+1). - Jon E. Schoenfield, Jun 03 2022
MAPLE
1, seq(4*n -simplify(ChebyshevU(n-1, -1/2)), n = 1..20); # G. C. Greubel, Apr 13 2021
MATHEMATICA
{1}~Join~LinearRecurrence[{1, 0, 1, -1}, {3, 9, 12, 15}, 59] (* Jean-François Alcover, Oct 23 2019 *)
PROG
(Magma) a:=[1, 3, 9, 12, 15]; [n le 5 select a[n] else Self(n-1)+Self(n-3)-Self(n-4):n in [1..60]]; // Marius A. Burtea, Oct 23 2019
(Sage) [1]+[4*n-chebyshev_U(n-1, -1/2) for n in (1..60)] # G. C. Greubel, Apr 13 2021
CROSSREFS
Sequence in context: A255686 A138921 A194412 * A244147 A103531 A333441
KEYWORD
nonn
AUTHOR
Colin Mallows, Apr 13 2008
EXTENSIONS
Entry revised by N. J. A. Sloane, Apr 06 2019, replacing the old definition with Colin Barker's recurrence.
STATUS
approved

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Last modified March 28 10:55 EDT 2024. Contains 371241 sequences. (Running on oeis4.)