OFFSET
1,2
LINKS
Colin Barker, Table of n, a(n) for n = 1..1000
Lara Pudwell, Systematic Studies in Pattern Avoidance, 2005.
Index entries for linear recurrences with constant coefficients, signature (9,-33,63,-66,36,-8)
FORMULA
G.f.: x*(1 - 7*x + 21*x^2 - 30*x^3 + 22*x^4 - 8*x^5) / ((1 - x)^3*(1 - 2*x)^3).
From Colin Barker, Oct 30 2017: (Start)
a(n) = (1/4)*(-4 + 2^(3+n) - (2+5*2^n)*n + (2+2^n)*n^2).
a(n) = 9*a(n-1) - 33*a(n-2) + 63*a(n-3) - 66*a(n-4) + 36*a(n-5) - 8*a(n-6) for n>6.
(End)
PROG
(PARI) Vec(x*(1 - 7*x + 21*x^2 - 30*x^3 + 22*x^4 - 8*x^5) / ((1 - x)^3*(1 - 2*x)^3) + O(x^40)) \\ Colin Barker, Oct 30 2017
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Lara Pudwell, Feb 26 2006
STATUS
approved