N = int(input())
A = list(map(int, input().split()))
Max = max(A);Min = min(A)
ans = 0
for k in range(1, Max - Min + 1):
    dp = [[0 for i in range(4)] for j in range(N)]
    for i in range(N):
        dp[i][0] = 1
        for j in range(i):
            if A[j] == A[i] - k - 10: dp[i][1] = dp[i][1] + dp[j][0]
            if A[j] == A[i] + k: dp[i][2] = dp[i][2] + dp[j][1]
            if A[j] == A[i] - 1 - k: dp[i][3] = dp[i][3] + dp[j][2]
    for i in range(N):
        ans = ans + dp[i][3]
print(ans)