N=int(input())
A=list(map(int,input().split()))
v=[0]*(4*10**5)
result=0
v2=[0]*(4*10**5)
for k in range(1,501):
  for i in range(N):
    x=A[i]-(i+1)*k
    if -2*10**5<x<2*10**5:
      result+=v[-x]
      v[x]+=1
  v=[0]*(4*10**5)
for i in range(1,N+1):
  c=min(N,800-i)
  for j in range(i+1,c+1):
    x,y=A[i-1],A[j-1]
    if (x+y)%(i+j)==0:
      z=(x+y)//(i+j)
      if z>500:
        result+=1
print(result)