OFFSET
0,1
FORMULA
I(n) = 1/(2*(n+1)) + 1/(2*3^(n+1)-1) * sum_{i=0}{n-1} (n choose i) 2^(n-i) I(i)
EXAMPLE
I(0) is obviously 1/2 by symmetry.
CROSSREFS
KEYWORD
frac,nonn
AUTHOR
Simon Tatham (anakin(AT)pobox.com), Apr 02 2009
STATUS
approved