|
|
A068979
|
|
Number of elements of rank n in the free lattice on three generators.
|
|
0
|
|
|
|
OFFSET
|
1,1
|
|
COMMENTS
|
The rank of a lattice term is the number of occurrences of variables in that term. The rank of an element is the minimum rank of a term representing that element.
|
|
LINKS
|
|
|
EXAMPLE
|
a(2) = 6 because the 6 elements of rank 2 are x + y, x + z, y + z, xy, xz and yz.
|
|
CROSSREFS
|
|
|
KEYWORD
|
more,nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|