91- 6303239042
Number of ways to divide n distinct objects into groups of specified sizes (with groups indistinguishable). Let there be k groups of size s1, m groups of size s2, etc. (so that k*s1 + m*s2 + ... = n). Then:
$$ \frac{n!}{(s_1!)^k (s_2!)^m \dots \times (k! m! \dots)} $$
