

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
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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 244.13 (2002): 4353. See Fig. 2.
Michel Deza and Mikhail Shtogrin, Isometric embedding of mosaics into cubic lattices, Discrete mathematics 244.13 (2002): 4353. [Annotated scan of page 52 only]
Michel Deza and Mikhail Shtogrin, Enlargement of figure from previous link
Chaim GoodmanStrauss and N. J. A. Sloane, A Coloring Book Approach to Finding Coordination Sequences, Acta Cryst. A75 (2019), 121134, 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).
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.


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 GoodmanStrauss  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(n1)  a(n2) + 2*a(n3)  a(n4) + a(n5)  a(n6) for n>6.
(End)


MATHEMATICA

Join[{1}, LinearRecurrence[{1, 1, 2, 1, 1, 1}, {4, 8, 8, 12, 20, 20}, 100]] (* JeanFrançois 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 * A333288 A159786 A083744
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



