OFFSET
0,2
LINKS
Index entries for linear recurrences with constant coefficients, signature (0,3,2,-1).
FORMULA
O.g.f.: (1+x)^2/(1-3x^2-2x^3+x^4)
EXAMPLE
a(6)=64-7=57 because 000011, 001111, 001100, 001101, 100110, 010011, 110011 are forbidden.
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Len Smiley, Nov 24 2001
STATUS
approved