_1175.java

package com.fishercoder.solutions;

/**
 * 1175. Prime Arrangements
 *
 * Return the number of permutations of 1 to n so that prime numbers are at prime indices (1-indexed.)
 * (Recall that an integer is prime if and only if it is greater than 1,
 * and cannot be written as a product of two positive integers both smaller than it.)
 * Since the answer may be large, return the answer modulo 10^9 + 7.
 *
 * Example 1:
 * Input: n = 5
 * Output: 12
 * Explanation: For example [1,2,5,4,3] is a valid permutation, but [5,2,3,4,1] is not because the prime number 5 is at index 1.
 *
 * Example 2:
 * Input: n = 100
 * Output: 682289015
 *
 * Constraints:
 * 1 <= n <= 100
 * */
public class _1175 {
    public static class Solution1 {
        public int numPrimeArrangements(int n) {
            //TODO: implement it
            return -1;
        }
    }
}