0,4

H. Bottomley & A. Karttunen Derivations of the formulae for the diagonals of A073345 & A073346.

a(n < 3) = 0, a(n) = ((n^2 - 6)*2^(n-2))

a(3) = 6 because there exists only these six binary trees of size 5 and height 3:

_\/\/_______\/\/_\/_\/_____\/_\/_\/___\/___V_V___

__\/_\/___\/_\/___\/_\/___\/_\/___\/_\/___\/_\/__

___\./_____\./_____\./_____\./_____\./_____\./___

A073773 := n -> `if`((n < 3), 0, ((n^2 - 6)*2^(n-2)));

A073773(n) = A073345(n+2, n). Cf. A014480, A073774, A028878.

Sequence in context: A002595 A089207 A027777 this_sequence A001919 A005553 A055344

Adjacent sequences: A073770 A073771 A073772 this_sequence A073774 A073775 A073776

nonn

Antti Karttunen Aug 11 2002