A316316 Coordination sequence for tetravalent node in chamfered version of square grid.

1, 4, 8, 8, 12, 20, 20, 20, 28, 32, 32, 36, 40, 44, 48, 48, 52, 60, 60, 60, 68, 72, 72, 76, 80, 84, 88, 88, 92, 100, 100, 100, 108, 112, 112, 116, 120, 124, 128, 128, 132, 140, 140, 140, 148, 152, 152, 156, 160, 164, 168, 168, 172, 180, 180, 180, 188, 192, 192

Offset: 0

Author

N. J. A. Sloane, Jun 29 2018

Keywords

• nonn
• easy

Links

• Rémy Sigrist, Table of n, a(n) for n = 0..5000
• Michel Deza and Mikhail Shtogrin, Isometric embedding of mosaics into cubic lattices, Discrete mathematics 244.1-3 (2002): 43-53. See Fig. 2.
• Michel Deza and Mikhail Shtogrin, Isometric embedding of mosaics into cubic lattices, Discrete mathematics 244.1-3 (2002): 43-53. [Annotated scan of page 52 only]
• Michel Deza and Mikhail Shtogrin, Enlargement of figure from previous link
• Chaim Goodman-Strauss and N. J. A. Sloane, A Coloring Book Approach to Finding Coordination Sequences, Acta Cryst. A75 (2019), 121-134, also on NJAS's home page. Also on arXiv, arXiv:1803.08530 [math.CO], 2018-2019.
• Rémy Sigrist, PARI program for A316316
• Rémy Sigrist, Illustration of first terms
• N. J. A. Sloane, Initial terms of coordination sequence for tetravalent node
• N. J. A. Sloane, Trunks and branches structure of tetravalent node (First part of proof that a(n+12)=a(n)+40).
• N. J. A. Sloane, Calculation of coordination sequence (Second part of proof that a(n+12)=a(n)+40).
• N. J. A. Sloane, "Basketweave" tiling by 3X1 rectangles which is equivalent (as far as the graph and coordination sequences are concerned) to this tiling
• N. J. A. Sloane, An equivalent tiling seen on the sidewalk of East 70th St in New York City. As far as the graph and coordination sequences are concerned, this is the same as the chamfered square grid. The trivalent vertices labeled b and c are equivalent to each other.
• Index entries for linear recurrences with constant coefficients, signature (1,-1,2,-1,1,-1).

Crossrefs

See A316317 for trivalent node.

See A250120 for links to thousands of other coordination sequences.

Cf. A316357 (partial sums).

Cf. A056594, A102283.

Programs

Mathematica

Join[{1}, LinearRecurrence[{1, -1, 2, -1, 1, -1}, {4, 8, 8, 12, 20, 20}, 100]] (* Jean-François Alcover, Dec 13 2018 *)

PARI

See Links section.

Formula

Apparently, a(n + 12) = a(n) + 40 for any n > 0. - Rémy Sigrist, Jun 30 2018

From N. J. A. Sloane, Jun 30 2018: This conjecture is true.

Theorem: a(n + 12) = a(n) + 40 for any n > 0.

The proof uses the Coloring Book Method described in the Goodman-Strauss - Sloane article. For details see the two links.

From Colin Barker, Dec 13 2018: (Start)

G.f.: (1 + 3*x + 5*x^2 + 2*x^3 + 5*x^4 + 3*x^5 + x^6) / ((1 - x)^2*(1 + x^2)*(1 + x + x^2)).

a(n) = a(n-1) - a(n-2) + 2*a(n-3) - a(n-4) + a(n-5) - a(n-6) for n>6.

(End)

a(n) = (2/9)*(15*n + 9*A056594(n-1) - 6*A102283(n)) for n > 0. - Stefano Spezia, Jun 12 2021

Extensions

More terms from Rémy Sigrist, Jun 30 2018