OFFSET
0,1
COMMENTS
Inverse binomial transform of A114491.
This sequence enumerates a certain type of matroid, except for the first entry (which is 2 instead of 1). If the first entry is changed from 2 to 1, giving A118085, this enumerates "combinatorial geometries" on n labeled points.
These are matroids in which no element has rank 0; equivalently, all one-element sets are independent; equivalently, the closure of the empty set is empty.
EXAMPLE
For all n>1, a function like "x2" is counted in A114491 but not in the present sequence.
CROSSREFS
KEYWORD
nonn
AUTHOR
Don Knuth, Aug 17 2008, Oct 14 2008
STATUS
approved