OFFSET
0,2
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..1000
Harry Crane, Left-right arrangements, set partitions, and pattern avoidance, Australasian Journal of Combinatorics, 61(1) (2015), 57-72.
Index entries for linear recurrences with constant coefficients, signature (9,-29,39,-18).
FORMULA
G.f.: 1/((1-x)*(1-2*x)*(1-3*x)^2).
a(n) = (1/4)*(2^(n+5) + (2*n - 3)*3^(n+2) - 1).
a(n) = 9*a(n-1) - 29*a(n-2) + 39*a(n-3) - 18*a(n-4).
E.g.f.: (1/4)*(32*exp(2*x) + 27*(2*x-1)*exp(3*x) - exp(x)). - G. C. Greubel, Aug 13 2017
MATHEMATICA
LinearRecurrence[{9, -29, 39, -18}, {1, 9, 52, 246}, 30] (* or *) CoefficientList[ Series[1/((1-x)(1-2x)(1-3x)^2), {x, 0, 30}], x] (* Harvey P. Dale, Aug 14 2011 *)
PROG
(PARI) Vec(1/((1-x)*(1-2*x)*(1-3*x)^2) + O(x^30)) \\ Michel Marcus, Feb 12 2015
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Johannes W. Meijer, Aug 13 2009
STATUS
approved