OFFSET
6,1
FORMULA
G.f.: 2*x^6*(1-2*x+3*x^2)*(1-x)^2/(1-2*x^5)/(1-2*x)^5= (1/(1-2*x)^5-1/(1-2*x^5))/5.
EXAMPLE
a(7) = 12 because 11111ab, 1111a1b, 111a11b where ab = 22, 23, 32 or 33 are all ternary Lyndon words of length 7 with five 1's.
MAPLE
a:= n-> (Matrix([[806, 224, 56, 12, 2, 0$5]]). Matrix(10, (i, j)-> `if`(i=j-1, 1, `if`(j=1, [10, -40, 80, -80, 34, -20, 80, -160, 160, -64] [i], 0)))^(n-10))[1, 1]: seq(a(n), n=6..30); # Alois P. Heinz, Aug 04 2008
CROSSREFS
KEYWORD
nonn
AUTHOR
Mike Zabrocki, Nov 05 2006
STATUS
approved