OFFSET
0,3
COMMENTS
Diagonal sums of number triangle A109960.
LINKS
Index entries for linear recurrences with constant coefficients, signature (4,-5,4,-1).
FORMULA
a(n)=sum{k=0..floor(n/2), binomial(n+2k, 4k)}.
a(0)=1, a(1)=1, a(2)=2, a(3)=6, a(n)=4*a(n-1)-5*a(n-2)+4*a(n-3)-a(n-4). - Harvey P. Dale, Dec 11 2013
MATHEMATICA
CoefficientList[Series[(1-3x+3x^2-x^3)/(1-4x+5x^2-4x^3+x^4), {x, 0, 40}], x] (* or *) LinearRecurrence[{4, -5, 4, -1}, {1, 1, 2, 6}, 40] (* Harvey P. Dale, Dec 11 2013 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Paul Barry, Jul 06 2005
STATUS
approved