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