OFFSET
0,2
FORMULA
A partition of {-n, ..., -1, 1, ..., n} into nonempty subsets X_1, ..., X_r is called `symmetric' if for each i -X_i = X_j for some j. S_D(n, k) is the number of such symmetric partitions whose induced partition on {1, ..., n} involves k nonempty subsets and none of the X_i are of the form {j, -j}.
CROSSREFS
KEYWORD
AUTHOR
James East, Sep 04 2003
STATUS
approved