from bisect import bisect_left,bisect_right
n = int(input())
a = list(map(int,input().split()))
b = [[] for _ in range(2001)]
for i,v in enumerate(a): b[v].append(i)
ans = 0
for i in range(n-1):
    for j in range(i+1,n):
        p = a[j]-10; q = a[i]+1; k = a[i]-p-10
        if 1<=p<=2000>=q>=1<=k: ans += bisect_left(b[p],i)*(len(b[q])-bisect_right(b[q],j))
print(ans)