**n-th Bell number of type D. 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. a(n) is the number of such symmetric partitions such that none of the X_i are of the form {j,-j}.**

*1, 4, 15, 75, 428, 2781, 20093, 159340, 1372163, 12725447, 126238060*

*4 seqfan posts*

Index of A-numbers in seqfan: by ascending order by month by frequency by keyword

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