import java.io.IOException;
import java.io.InputStream;
import java.util.*;
import java.util.function.BiFunction;
import java.util.function.Function;
import java.util.function.Supplier;
public class Main {
void run() {
int n = ni();
int[] a = new int[n];
TreeSet<Integer> set = new TreeSet<>();
for (int i = 0; i < n; ++i) {
a[i] = ni();
set.add(a[i]);
}
if (a[0] != 0) {
System.out.println(0);
return;
}
for (int i = 1; i < n; ++i) {
if (a[i] == 0) {
System.out.println(0);
return;
}
}
int v = 0;
while (set.size() > 0) {
int w = set.pollFirst();
if (v != w) {
System.out.println(0);
return;
}
v++;
}
if (v == 1) {
System.out.println(1);
return;
}
int[] size = new int[v];
for (int i = 0; i < n; ++i) {
size[a[i]]++;
}
TreeMap<Node, Long> map = new TreeMap<>();
long seki = 1;
for (int i = 2; i < v; ++i) {
int N = size[i - 1];
int M = size[i];
long sub = pow(2, (long) N * (N - 1) / 2);
sub *= pow(pow(2, N) - 1, M);
sub %= MOD;
seki *= sub;
seki %= MOD;
}
seki *= pow(2, (long) size[v - 1] * (size[v - 1] - 1) / 2);
seki %= MOD;
System.out.println(seki);
}
class Node implements Comparable<Node> {
int n, m;
Node(int n, int m) {
this.n = n;
this.m = m;
}
@Override
public int hashCode() {
return n ^ m;
}
@Override
public int compareTo(Node node) {
if (n == node.n) {
return m - node.m;
} else {
return n - node.n;
}
}
@Override
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (this.getClass() != o.getClass()) {
return false;
}
Node node = (Node) o;
return n == node.n && m == node.m;
}
}
Scanner sc = new Scanner(System.in);
public static void main(String[] args) {
new Main().run();
}
int ni() {
return Integer.parseInt(sc.next());
}
void debug(Object... os) {
System.err.println(Arrays.deepToString(os));
}
class BIT<T> {
int n;
ArrayList<T> bit;
BiFunction<T, T, T> bif;
/**
* 1-indexed なBinary Indexed Treeを構築する
*
* @param n 容量
* @param bif 適用させる関数
* @param sup 初期値
*/
BIT(int n, BiFunction<T, T, T> bif, Supplier<T> sup) {
this.n = n;
bit = new ArrayList<>(n + 1);
for (int i = 0; i < n + 1; ++i) {
bit.add(sup.get());
}
this.bif = bif;
}
/**
* iの位置の値をvで更新する
*
* @param i index
* @param v 新しい値
*/
void update(int i, T v) {
for (int x = i; x <= n; x += x & -x) {
bit.set(x, bif.apply(bit.get(x), v));
}
}
/**
* クエリー
*
* @param defaultValue 初期値
* @param i index
* @return [1, i]までfを適用した結果
*/
T reduce(T defaultValue, int i) {
T ret = defaultValue;
for (int x = i; x > 0; x -= x & -x) {
ret = bif.apply(ret, bit.get(x));
}
return ret;
}
}
long MOD = 1_000_000_007;
/**
* 繰り返し2乗法を用いたべき乗の実装
*
* @return a^r (mod 1,000,000,007)
*/
long pow(long a, long r) {
long sum = 1;
while (r > 0) {
if ((r & 1) == 1) {
sum *= a;
sum %= MOD;
}
a *= a;
a %= MOD;
r >>= 1;
}
return sum;
}
/**
* 組み合わせ
* O(n)
*
* @return {}_nC_r
*/
long C(int n, int r) {
long sum = 1;
for (int i = n; 0 < i; --i) {
sum *= i;
sum %= MOD;
}
long s = 1;
for (int i = r; 0 < i; --i) {
s *= i;
s %= MOD;
}
sum *= pow(s, MOD - 2);
sum %= MOD;
long t = 1;
for (int i = n - r; 0 < i; --i) {
t *= i;
t %= MOD;
}
sum *= pow(t, MOD - 2);
sum %= MOD;
return sum;
}
double GOLDEN_RATIO = (1.0 + Math.sqrt(5)) / 2.0;
/**
* 黄金分割探索
*
* @param left 下限
* @param right 上限
* @param f 探索する関数
* @param comp 上に凸な関数を探索するときは、Comparator.comparingDouble(Double::doubleValue)
* 下に凸な関数を探索するときは、Comparator.comparingDouble(Double::doubleValue).reversed()
* @return 極値の座標x
*/
double goldenSectionSearch(double left, double right, Function<Double, Double> f, Comparator<Double> comp) {
double c1 = divideInternally(left, right, 1, GOLDEN_RATIO);
double c2 = divideInternally(left, right, GOLDEN_RATIO, 1);
double d1 = f.apply(c1);
double d2 = f.apply(c2);
while (right - left > 1e-9) {
if (comp.compare(d1, d2) > 0) {
right = c2;
c2 = c1;
d2 = d1;
c1 = divideInternally(left, right, 1, GOLDEN_RATIO);
d1 = f.apply(c1);
} else {
left = c1;
c1 = c2;
d1 = d2;
c2 = divideInternally(left, right, GOLDEN_RATIO, 1);
d2 = f.apply(c2);
}
}
return right;
}
/**
* [a,b]をm:nに内分する点を返す
*/
double divideInternally(double a, double b, double m, double n) {
return (n * a + m * b) / (m + n);
}
/**
* http://qiita.com/p_shiki37/items/65c18f88f4d24b2c528b
*/
static class FastScanner {
private final InputStream in;
private final byte[] buffer = new byte[1024];
private int ptr = 0;
private int buflen = 0;
public FastScanner(InputStream in) {
this.in = in;
}
private boolean hasNextByte() {
if (ptr < buflen) {
return true;
} else {
ptr = 0;
try {
buflen = in.read(buffer);
} catch (IOException e) {
e.printStackTrace();
}
if (buflen <= 0) {
return false;
}
}
return true;
}
private int readByte() {
if (hasNextByte()) return buffer[ptr++];
else return -1;
}
private static boolean isPrintableChar(int c) {
return 33 <= c && c <= 126;
}
private void skipUnprintable() {
while (hasNextByte() && !isPrintableChar(buffer[ptr])) ptr++;
}
public boolean hasNext() {
skipUnprintable();
return hasNextByte();
}
public String next() {
if (!hasNext()) throw new NoSuchElementException();
StringBuilder sb = new StringBuilder();
int b = readByte();
while (isPrintableChar(b)) {
sb.appendCodePoint(b);
b = readByte();
}
return sb.toString();
}
public long nextLong() {
if (!hasNext()) throw new NoSuchElementException();
long n = 0;
boolean minus = false;
int b = readByte();
if (b == '-') {
minus = true;
b = readByte();
}
if (b < '0' || '9' < b) {
throw new NumberFormatException();
}
while (true) {
if ('0' <= b && b <= '9') {
n *= 10;
n += b - '0';
} else if (b == -1 || !isPrintableChar(b)) {
return minus ? -n : n;
} else {
throw new NumberFormatException();
}
b = readByte();
}
}
}
}