n=int(input())
a=list(map(int,input().split()))
A=max(a)
g=0
for k in range(1,A):
	q=[[0]*(A+1) for _ in range(3)]
	for i in range(n):
		if a[i]-k-1>=0:
			g+=q[2][a[i]-k-1]
		if a[i]+k<=A:
			q[2][a[i]]+=q[1][a[i]+k]
		if a[i]-k-10>=0:
			q[1][a[i]]+=q[0][a[i]-k-10]
		q[0][a[i]]+=1
print(g)