{n\brack k}Stirling numbers of the first kind, denoted as {n\brack k}, count the number of permutations of n elements with exactly k permutation cycles. They are used in combinatorics to study permutations and their properties.
The number of permutations of 5 elements with exactly 2 cycles.
{5\brack 2} = 50The number of permutations of 4 elements with exactly 1 cycle.
{4\brack 1} = 6The number of permutations of 6 elements with exactly 3 cycles.
{6\brack 3} = 90