OFFSET
0,4
LINKS
Henry Bottomley & Antti Karttunen Derivations of the formulas for the diagonals of A073345 & A073346.
FORMULA
a(n) = A073345(n+2, n).
a(n < 3) = 0, a(n) = ((n^2 - 6)*2^(n-2)).
EXAMPLE
a(3) = 6 because there exists only these six binary trees of size 5 and height 3:
_\/\/_______\/\/_\/_\/_____\/_\/_\/___\/___V_V___
__\/_\/___\/_\/___\/_\/___\/_\/___\/_\/___\/_\/__
___\./_____\./_____\./_____\./_____\./_____\./___
MAPLE
A073773 := n -> `if`((n < 3), 0, ((n^2 - 6)*2^(n-2)));
CROSSREFS
KEYWORD
nonn
AUTHOR
Antti Karttunen, Aug 11 2002
STATUS
approved