/**
 * Calculates the number of permutations (nPk).
 * @param {number} n - The total number of items.
 * @param {number} [k] - The number of items to arrange.
 * @returns The number of possible permutations.
 * @example
 * perm(3, 2); // 6
*/
export declare function perm(n: number, k?: number): number;