pub mod scanner {

    pub struct Scanner {
        buf: Vec<String>,
    }

    impl Scanner {
        pub fn new() -> Self {
            Self { buf: vec![] }
        }

        pub fn new_from(source: &str) -> Self {
            let source = String::from(source);
            let buf = Self::split(source);
            Self { buf }
        }

        pub fn next<T: std::str::FromStr>(&mut self) -> T {
            loop {
                if let Some(x) = self.buf.pop() {
                    return x.parse().ok().expect("");
                }
                let mut source = String::new();
                std::io::stdin().read_line(&mut source).expect("");
                self.buf = Self::split(source);
            }
        }

        fn split(source: String) -> Vec<String> {
            source
                .split_whitespace()
                .rev()
                .map(String::from)
                .collect::<Vec<_>>()
        }
    }
}

use crate::scanner::Scanner;
use std::io::Write;
fn main() {
    let mut scanner = Scanner::new();
    let out = std::io::stdout();
    let mut out = std::io::BufWriter::new(out.lock());
    let t: usize = 1;
    for _ in 0..t {
        solve(&mut scanner, &mut out);
    }
}
fn solve(scanner: &mut Scanner, out: &mut std::io::BufWriter<std::io::StdoutLock>) {
    const MAX: usize = 2000;
    let n: usize = scanner.next();
    let a = (0..n).map(|_| scanner.next::<usize>()).collect::<Vec<_>>();
    let mut count = vec![0usize; MAX + 10];
    for i in 2..n {
        count[a[i]] += 1;
    }
    let mut dp = vec![vec![0usize; MAX + 10]; MAX + 10];
    let mut ans: usize = 0;
    for i in 1..n - 1 {
        if a[i] > 10 {
            let a1 = a[i] - 10;
            for k in 1..=MAX - a[i] {
                ans += dp[a1][k] * count[a[i] + k + 1];
            }
        }
        for j in 0..i {
            if a[j] + 10 < a[i] {
                dp[a[j]][a[i] - a[j] - 10] += 1;
            }
        }
        count[a[i + 1]] -= 1;
    }
    writeln!(out, "{}", ans).unwrap();
}