# https://yukicoder.me/problems/no/2374

from collections import deque

def main():
    N = int(input())
    A = list(map(int, input().split()))

    answer = 0
    stock_map = {}
    for i in reversed(range(N)):
        a2 = A[i]

        for j in range(i):
            a1 = A[j]
            k = a2 - a1 -10
            if k > 0:
                a3 = (a2 - k)
                a4 = a3 + k + 1
                if (a3, a4) in stock_map:
                    answer += stock_map[(a3, a4)]
        
        a3 = a2
        for j in range(i + 1, N):
            a4 = A[j]
            if (a3, a4) not in stock_map:
                stock_map[(a3, a4)] = 0
            stock_map[(a3, a4)] += 1
    print(answer)
    

            




if __name__ == "__main__":
    main()