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A068979 Number of elements of rank n in the free lattice on three generators. 0
3, 6, 8, 18, 18, 56, 126, 282, 686, 1806 (list; graph; refs; listen; history; text; internal format)
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

Table of n, a(n) for n=1..10.

EXAMPLE

a(2) = 6 because the 6 elements of rank 2 are x + y, x + z, y + z, xy, xz and yz.

CROSSREFS

Sequence in context: A179652 A253855 A298860 * A101060 A278486 A038064

Adjacent sequences:  A068976 A068977 A068978 * A068980 A068981 A068982

KEYWORD

more,nonn

AUTHOR

David Wasserman, Mar 31 2002

STATUS

approved

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Last modified April 19 08:58 EDT 2019. Contains 322241 sequences. (Running on oeis4.)