#!/bin/python

import sys
import itertools
import itertools

n = int(raw_input().strip())
m = map(int, raw_input().strip().split(' '))
# your code goes here

def get_array_combinations(n, m):
    arrays = []
    for l in range(1, n + 1):
        for subset in itertools.combinations(m, l):
            arrays.append(list(subset))

    # print arrays
    combs = []
    for l in range(1, n + 1):
        # print l
        for subset in itertools.combinations(arrays, l):
            combs.append(list(subset))
            # print list(subset)
    return combs


def test_array(array):
    m = []
    i = 0
    coll = []
    max_elem_len = len(max(array, key=len))
    while i < max_elem_len:
        tmp = []
        for a in array:
            a_len = len(a)
            if i < a_len:
                tmp.append(a[i])
        coll.append(tmp)
        i += 1
    for c in coll:
        c.sort()
        m += c
    # print 'c =', coll
    # print 'm =', m
    return m


def my_main(m, n):
    combs = get_array_combinations(n, m)
    # t_arr = [[3, 5], [1], [2, 4]]
    # t_arr = [[2,1]]
    i = 0
    for c in combs:
        m_test = test_array(c)
        if m_test == m:
            i += 1
    print i % 1000000007

my_main(m, n)