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 (3,-3,1).
FORMULA
G.f.: x*(1 - x + 2*x^2 + 2*x^3 - 2*x^5) / (1 - x)^3.
For n >= 4, a(n) = n^2 + 2*n - 12. - Franklin T. Adams-Watters, Sep 16 2006
a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3) for n>3. - Colin Barker, Oct 23 2017
PROG
(PARI) Vec(x*(1 - x + 2*x^2 + 2*x^3 - 2*x^5) / (1 - x)^3 + O(x^50)) \\ Colin Barker, Oct 23 2017
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Lara Pudwell, Feb 26 2006
STATUS
approved