OFFSET
0,2
COMMENTS
Diagonal sums of number triangle A128414.
LINKS
Colin Barker, Table of n, a(n) for n = 0..1000
Index entries for linear recurrences with constant coefficients, signature (-4,-3).
FORMULA
G.f.: (1-4*x^2)/(1+4*x+3*x^2).
For n > 1, |a(n)| = 3*(|a(n-1)| - 1). - Tamas Kalmar-Nagy (integers(AT)kalmarnagy.com), Sep 17 2010
From Colin Barker, Sep 21 2016: (Start)
a(n) = (-1)^n*(9+5*3^n)/6 for n>0.
a(n) = -4*a(n-1)-3*a(n-2) for n>2. (End)
PROG
(PARI) Vec((1-4*x^2)/(1+4*x+3*x^2) + O(x^30)) \\ Colin Barker, Sep 21 2016
CROSSREFS
KEYWORD
easy,sign
AUTHOR
Paul Barry, Mar 02 2007
STATUS
approved