OFFSET
1,2
LINKS
Colin Barker, Table of n, a(n) for n = 1..1000
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 83.
Lara Pudwell, Systematic Studies in Pattern Avoidance, 2005.
Index entries for linear recurrences with constant coefficients, signature (9,-32,56,-48,16).
FORMULA
G.f.: x*(1 - 7*x + 20*x^2 - 25*x^3 + 12*x^4 - 2*x^5 - x^6) / ((1 - x)*(1 - 2*x)^4).
a(n) = (1/128)*(4*(-64 + 65*2^n) - 107*2^n*n + 9*2^(1+n)*n^2 + 2^n*n^3) for n > 2. - Colin Barker, Nov 02 2017
MATHEMATICA
CoefficientList[Series[(1 - 7*x + 20*x^2 - 25*x^3 + 12*x^4 - 2*x^5 - x^6)/((1 - x)*(1 - 2*x)^4), {x, 0, 40}], x] (* Wesley Ivan Hurt, Dec 26 2023 *)
PROG
(PARI) Vec(x*(1 - 7*x + 20*x^2 - 25*x^3 + 12*x^4 - 2*x^5 - x^6) / ((1 - x)*(1 - 2*x)^4) + O(x^30)) \\ Colin Barker, Nov 02 2017
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Lara Pudwell, Feb 26 2006
STATUS
approved