OFFSET
0,2
COMMENTS
Also known as the kgd net.
This is one of the Laves tilings.
LINKS
Robert Israel, Table of n, a(n) for n = 0..10000
Reticular Chemistry Structure Resource (RCSR), The kgd tiling (or net)
N. J. A. Sloane, Overview of coordination sequences of Laves tilings [Fig. 2.7.1 of Grünbaum-Shephard 1987 with A-numbers added and in some cases the name in the RCSR database]
Index entries for linear recurrences with constant coefficients, signature (0,2,0,-1).
FORMULA
a(0)=1; a(2*k)=6*k, a(2*k+1)=12*k+6.
G.f.: 1 + 6*x*(1+x+x^2)/(1-x^2)^2. - Robert Israel, Jan 21 2018
From Colin Barker, Jan 22 2018: (Start)
a(n) = 3*n for n>0 and even.
a(n) = 6*n for n odd.
a(n) = 2*a(n-2) - a(n-4) for n>4.
(End)
a(n) = 6*A026741(n), n>0. - R. J. Mathar, Jan 29 2018
MAPLE
f6:=proc(n) if n=0 then 1 elif (n mod 2) = 0 then 3*n else 6*n; fi; end;
[seq(f6(n), n=0..80)];
MATHEMATICA
Join[{1}, LinearRecurrence[{0, 2, 0, -1}, {6, 6, 18, 12}, 80]] (* Jean-François Alcover, Mar 23 2020 *)
PROG
(PARI) Vec((1 + 6*x + 4*x^2 + 6*x^3 + x^4) / ((1 - x)^2*(1 + x)^2) + O(x^60)) \\ Colin Barker, Jan 22 2018
CROSSREFS
List of coordination sequences for Laves tilings (or duals of uniform planar nets): [3,3,3,3,3.3] = A008486; [3.3.3.3.6] = A298014, A298015, A298016; [3.3.3.4.4] = A298022, A298024; [3.3.4.3.4] = A008574, A296368; [3.6.3.6] = A298026, A298028; [3.4.6.4] = A298029, A298031, A298033; [3.12.12] = A019557, A298035; [4.4.4.4] = A008574; [4.6.12] = A298036, A298038, A298040; [4.8.8] = A022144, A234275; [6.6.6] = A008458.
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Jan 21 2018
STATUS
approved