Stirling number of the 2nd kind of k-partitions of an n-set }-{"}{-} Case.I In}is not a partition block n is in one of the blocks in a k-partition of [n-1] Case.2 In}is a partition block the remaining 1 blocks forms a (%1)-partition of [n-1]Stirling number of the 2nd kind # of k-partitions of an n-set ￾n k ￾ ￾n k ￾ = k ￾n ￾ 1 k ￾ + ￾n ￾ 1 k ￾ 1 ￾ Case.1 Case.2 {n} is a partition block {n} is not a partition block n is in one of the k blocks in a k-partition of [n-1] the remaining k-1 blocks forms a (k-1)-partition of [n-1]