OFFSET
0,2
COMMENTS
Row sums of A102435. The number of matchings of the ladder graph L(n)=P_2 X P_n is given in A030186.
Number of tilings of a 2xn board with squares of 2 colors and dominoes of 1 color [Katz-Stenson]. - R. J. Mathar, Apr 17 2009
LINKS
Colin Barker, Table of n, a(n) for n = 0..1000
M. Katz, C. Stenson, Tiling a 2xn-board with squares and dominoes, J. Int. Seq. 12 (2009) # 09.2.2
Index entries for linear recurrences with constant coefficients, signature (6,4,-1).
FORMULA
a(n) = 6*a(n-1) + 4*a(n-2) - a(n-3) for n>=3.
G.f.: (1-x) / (1-6*x-4*x^2+x^3).
EXAMPLE
a(2)=34 because in the graph L'(2) with vertex set {A,B,C,D,a,b,c,d} and edge set {AB,BC,CD,AD,Aa,Bb,Cc,Dd} we have one 0-matching (the empty set), eight 1-matchings (each edge as a singleton), sixteen 2-matchings (see Example in A102435), eight 3-matchings (any 3-element subset of {Aa,Bb,Cc,Dd} and {Aa,Bb,CD},{Bb,Cc,AD},{Cc,Dd,AB},{Aa,Dd,BC}) and one 4-matching ({Aa,Bb,Cc,Dd}).
MAPLE
a[0]:=1: a[1]:=5: a[2]:=34: for n from 3 to 24 do a[n]:=6*a[n-1]+4*a[n-2] -a[n-3] od: seq(a[n], n=0..24);
MATHEMATICA
LinearRecurrence[{6, 4, -1}, {1, 5, 34}, 30] (* G. C. Greubel, Oct 27 2019 *)
PROG
(PARI) Vec((1 - x) / (1 - 6*x - 4*x^2 + x^3) + O(x^30)) \\ Colin Barker, Jun 06 2017
(Magma) I:=[1, 5, 34]; [n le 3 select I[n] else 6*Self(n-1) +4*Self(n-2) -Self(n-3): n in [1..30]]; // G. C. Greubel, Oct 27 2019
(Sage)
def A102436_list(prec):
P.<x> = PowerSeriesRing(ZZ, prec)
return P((1-x)/(1-6*x-4*x^2+x^3)).list()
A102436_list(30) # G. C. Greubel, Oct 27 2019
(GAP) a:=[1, 5, 34];; for n in [4..30] do a[n]:=6*a[n-1]+4*a[n-2]-a[n-3]; od; a; # G. C. Greubel, Oct 27 2019
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Emeric Deutsch, Jan 08 2005
STATUS
approved