import java.util.*;

public class Main {
    static final int MOD = 1000000007;
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] arr = new int[n + 1];
        for (int i = 1; i <= n; i++) {
            arr[i] = sc.nextInt();
        }
        int[] dp = new int[n + 1];
        dp[1] = 1;
        int add = 0;
        for (int i = 1; i < n; i++) {
            dp[i] += add;
            dp[i] %= MOD;
            if (arr[i] == 1) {
                add += dp[i];
                add %= MOD;
            } else {
                dp[i + 1] += dp[i];
                dp[i + 1] %= MOD;
                for (int j = 1; i + j * arr[i] <= n; j++) {
                    dp[i + j * arr[i]] += dp[i];
                    dp[i + j * arr[i]] %= MOD;
                }
            }
        }
        System.out.println((dp[n] + add) % MOD);
    }
}