OFFSET
0,3
LINKS
Index entries for linear recurrences with constant coefficients, signature (2,1,-2,-1,0,1).
FORMULA
G.f.: (1-x-x^2)/((1+x)(1-x)^2(1-x-x^2-x^3)); a(n)=2a(n-1)+a(n-2)-2a(n-3)-a(n-4)+a(n-6); a(n)=sum{k-0..floor(n/2), sum{j=0..n-2k, C(k, j)C(n-k-j, k)*(1+(-1)^j)/2}}.
MATHEMATICA
LinearRecurrence[{2, 1, -2, -1, 0, 1}, {1, 1, 2, 3, 5, 8}, 40] (* Harvey P. Dale, Nov 24 2017 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Paul Barry, May 31 2005
STATUS
approved