|
|
A060548
|
|
a(n) is the number of D3-symmetric patterns that may be formed with a top-down equilateral triangular arrangement of closely packed black and white cells satisfying the local matching rule of Pascal's triangle modulo 2, where n is the number of cells in each edge of the arrangement. The matching rule is such that any elementary top-down triangle of three neighboring cells in the arrangement contains either one or three white cells.
|
|
6
|
|
|
2, 1, 2, 2, 2, 2, 4, 2, 4, 4, 4, 4, 8, 4, 8, 8, 8, 8, 16, 8, 16, 16, 16, 16, 32, 16, 32, 32, 32, 32, 64, 32, 64, 64, 64, 64, 128, 64, 128, 128, 128, 128, 256, 128, 256, 256, 256, 256, 512, 256, 512, 512, 512, 512, 1024, 512, 1024, 1024, 1024, 1024, 2048, 1024, 2048
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
LINKS
|
|
|
FORMULA
|
a(n) = 2^{floor[(n+3)/6]+d(n)}, with d(n)=1 if n mod 6=1, else d(n)=0.
a(n) = a(n-2)a(n-3)/a(n-5), n>5.
Conjecture: a(n)=2*a(n-6) for n>1. G.f.: -x*(2*x^5+2*x^4+2*x^3+2*x^2+x+2) / (2*x^6-1). - Colin Barker, Aug 29 2013
|
|
MATHEMATICA
|
a[n_] := a[n] = a[n-2]*a[n-3]/a[n-5]; a[1] = a[3] = a[4] = a[5] = 2; a[2] = 1; Table[a[n], {n, 1, 63}] (* Jean-François Alcover, Dec 27 2011, after second formula *)
LinearRecurrence[{0, 0, 0, 0, 0, 2}, {2, 1, 2, 2, 2, 2}, 70] (* Harvey P. Dale, Sep 19 2016 *)
|
|
PROG
|
(PARI) a(n)=if(n<1, 0, 2^((n+3)\6+(n%6==1)))
(PARI) { for (n=1, 500, write("b060548.txt", n, " ", 2^((n + 3)\6 + (n%6==1))); ) } \\ Harry J. Smith, Jul 07 2009
|
|
CROSSREFS
|
|
|
KEYWORD
|
easy,nice,nonn
|
|
AUTHOR
|
André Barbé (Andre.Barbe(AT)esat.kuleuven.ac.be), Apr 02 2001
|
|
STATUS
|
approved
|
|
|
|