import java.io.*;
import java.util.*;
import java.util.stream.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner();
        int n = sc.nextInt();
        int[] values = new int[n];
        for (int i = 0; i < n; i++) {
            values[i] = sc.nextInt();
        }
        long ans = 0;
        for (int i = 1; i <= 2000; i++) {
            int[] add = new int[]{-i - 10, i, -i - 1};
            ArrayList<HashMap<Integer, Long>> counts = new ArrayList<>();
            for (int j = 0; j < 4; j++) {
                counts.add(new HashMap<>());
            }
            for (int x : values) {
                for (int j = 2; j >= 0; j--) {
                    if (counts.get(j).containsKey(x + add[j])) {
                        counts.get(j + 1).put(x, counts.get(j + 1).getOrDefault(x, 0L) + counts.get(j).get(x + add[j]));
                    }
                }
                counts.get(0).put(x, counts.get(0).getOrDefault(x, 0L) + 1);
            }
            for (long x : counts.get(3).values()) {
                ans += x;
            }
        }
        System.out.println(ans);
    }
}
class Utilities {
    static String arrayToLineString(Object[] arr) {
        return Arrays.stream(arr).map(x -> x.toString()).collect(Collectors.joining("\n"));
    }
    
    static String arrayToLineString(int[] arr) {
        return String.join("\n", Arrays.stream(arr).mapToObj(String::valueOf).toArray(String[]::new));
    }
}
class Scanner {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    StringTokenizer st = new StringTokenizer("");
    StringBuilder sb = new StringBuilder();
    
    public Scanner() throws Exception {
        
    }
    
    public int nextInt() throws Exception {
        return Integer.parseInt(next());
    }
    
    public long nextLong() throws Exception {
        return Long.parseLong(next());
    }
    
    public double nextDouble() throws Exception {
        return Double.parseDouble(next());
    }
    
    public int[] nextIntArray() throws Exception {
        return Stream.of(br.readLine().split(" ")).mapToInt(Integer::parseInt).toArray();
    }
    
    public String next() throws Exception {
        while (!st.hasMoreTokens()) {
            st = new StringTokenizer(br.readLine());
        }
        return st.nextToken();
    }
    
}