OFFSET
2,2
LINKS
Index entries for linear recurrences with constant coefficients, signature (2,2,-2,-4).
FORMULA
G.f.: x^2/((1-2*x)*(1-2*x^2-2*x^3)).
EXAMPLE
a(4) = 6 because of 0100, 0101, 1010, 1101, 0111, 0001.
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Len Smiley, Nov 24 2001
STATUS
approved