OFFSET
0,3
LINKS
C. Bean, M. Tannock and H. Ulfarsson, Pattern avoiding permutations and independent sets in graphs, arXiv:1512.08155 [math.CO], 2015, eq. (4).
D. Callan, T. Mansour, Enumeration of small Wilf classes avoiding 1324 and two other 4-letter patterns, arXiv:1705.00933 [math.CO] (2017), Table 2 No 181.
Index entries for linear recurrences with constant coefficients, signature (4,-2,2,-1).
FORMULA
G.f.: (2*x^3 + 3*x - 1)/(-x^4 + 2*x^3 - 2*x^2 + 4*x - 1).
MAPLE
t1:=(1-3*x-2*x^3)/(1-4*x+2*x^2-2*x^3+x^4);
series(t1, x, 40);
seriestolist(%); # N. J. A. Sloane, Nov 09 2016
MATHEMATICA
LinearRecurrence[{4, -2, 2, -1}, {1, 1, 2, 6}, 30] (* Jean-François Alcover, Dec 31 2015 *)
CoefficientList[Series[(2 x^3 + 3 x - 1)/(-x^4 + 2*x^3 - 2 x^2 + 4 x - 1), {x, 0, 35}], x] (* Vincenzo Librandi, Jan 01 2016 *)
PROG
(PARI) Vec((2*x^3 + 3*x - 1)/(-x^4 + 2*x^3 - 2*x^2 + 4*x - 1) + O(x^50)) \\ Michel Marcus, Nov 23 2015
(Magma) I:=[1, 1, 2, 6]; [n le 4 select I[n] else 4*Self(n-1)-2*Self(n-2)+2*Self(n-3)-Self(n-4): n in [1..40]]; // Vincenzo Librandi, Jan 01 2016
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Christian Bean, Nov 23 2015
STATUS
approved