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A316316 Coordination sequence for tetravalent node in chamfered version of square grid. 3
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

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

C. 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 arXiv:1803.08530.

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).

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.

Conjectures 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)

MATHEMATICA

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

PROG

(PARI) See Links section.

CROSSREFS

See A316317 for trivalent node.

See A250120 for links to thousands of other coordination sequences.

Cf. A316357 (partial sums).

Sequence in context: A299771 A294963 A014198 * A159786 A083744 A255992

Adjacent sequences:  A316313 A316314 A316315 * A316317 A316318 A316319

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Jun 29 2018

EXTENSIONS

More terms from Rémy Sigrist, Jun 30 2018

STATUS

approved

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Last modified March 18 22:11 EDT 2019. Contains 321305 sequences. (Running on oeis4.)