/**
 * Calculates combinations with repetition (nHr) - ways to choose r items from n items with repetition allowed
 * @param n - Total number of items
 * @param r - Number of items to choose
 * @returns {number} Number of combinations with repetition, or NaN for invalid arguments
 * @example nHr(5, 2); // 15
 * @description
 * Also known as "stars and bars" problem or "multichoose".
 * Uses the formula nHr = (n+r-1)Cr
 */
export declare const nHr: (n: number, r: number) => number;