Buggy python submission (verdict: Time Limit Exceeded):
def n0():return int(input())
def n1():return [int(x) for x in input().split()]
def n2(n):return [int(input()) for _ in range(n)]
def n3(n):return [[int(x) for x in input().split()] for _ in range(n)]

from collections import defaultdict
n=n0()
a=[0]
a.extend(n1())

m1=[i+a[i] for i in range(n+1)]
m2=[j-a[j] for j in range(n+1)]

d1=defaultdict(list)
d2=defaultdict(list)
for i in range(1,n+1):
    d1[m1[i]].append(i)
    d2[m2[i]].append(i)

ans=0
for i in d1:
    if len(d2[i])>0:
        for k in d1[i]:
            ans+=len([h for h in d2[i] if h>k])
print(ans)

Fixed submission:
def n0():return int(input())
def n1():return [int(x) for x in input().split()]
def n2(n):return [int(input()) for _ in range(n)]
def n3(n):return [[int(x) for x in input().split()] for _ in range(n)]

from collections import defaultdict
n=n0()
a=[0]
a.extend(n1())

m1=[i+a[i] for i in range(n+1)]
m2=[j-a[j] for j in range(n+1)]

d1=defaultdict(list)
d2=defaultdict(list)
for i in range(1,n+1):
    d1[m1[i]].append(i)
    d2[m2[i]].append(i)

ans=0
for i in d1:
    ans+=len(d1[i])*len(d2[i])
            
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
def n0():return int(input())
def n1():return [int(x) for x in input().split()]
def n2(n):return [int(input()) for _ in range(n)]
def n3(n):return [[int(x) for x in input().split()] for _ in range(n)]

from collections import defaultdict
n=n0()
a=[0]
a.extend(n1())

m1=[i+a[i] for i in range(n+1)]
m2=[j-a[j] for j in range(n+1)]

d1=defaultdict(list)
d2=defaultdict(list)
for i in range(1,n+1):
    d1[m1[i]].append(i)
    d2[m2[i]].append(i)

ans=0
for i in d1:
    if len(d2[i])>0:
        for k in d1[i]:
            ans+=len([h for h in d2[i] if h>k])
print(ans)

Fixed submission:
def n0():return int(input())
def n1():return [int(x) for x in input().split()]
def n2(n):return [int(input()) for _ in range(n)]
def n3(n):return [[int(x) for x in input().split()] for _ in range(n)]

from collections import defaultdict
n=n0()
a=[0]
a.extend(n1())

m1=[i+a[i] for i in range(n+1)]
m2=[j-a[j] for j in range(n+1)]

d1=defaultdict(list)
d2=defaultdict(list)
for i in range(1,n+1):
    d1[m1[i]].append(i)
    d2[m2[i]].append(i)

ans=0
for i in d1:
    ans+=len(d1[i])*len(d2[i])
            
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
def n0():return int(input())
def n1():return [int(x) for x in input().split()]
def n2(n):return [int(input()) for _ in range(n)]
def n3(n):return [[int(x) for x in input().split()] for _ in range(n)]

n=n0()
a=n1()

ans=0
for i in range(n):
    h=a[i]
    B=list(range(-i,-i+n))
    C=[0]*n
    for j in range(n):
        C[j]=abs(B[j])-a[j]-h
    ans+=C.count(0)
print(ans//2)

Fixed submission:
def n0():return int(input())
def n1():return [int(x) for x in input().split()]
def n2(n):return [int(input()) for _ in range(n)]
def n3(n):return [[int(x) for x in input().split()] for _ in range(n)]

from collections import defaultdict
n=n0()
a=[0]
a.extend(n1())

m1=[i+a[i] for i in range(n+1)]
m2=[j-a[j] for j in range(n+1)]

d1=defaultdict(list)
d2=defaultdict(list)
for i in range(1,n+1):
    d1[m1[i]].append(i)
    d2[m2[i]].append(i)

ans=0
for i in d1:
    ans+=len(d1[i])*len(d2[i])
            
print(ans)

Buggy python submission (verdict: Runtime Error):
def n0():return int(input())
def n1():return [int(x) for x in input().split()]
def n2(n):return [int(input()) for _ in range(n)]
def n3(n):return [[int(x) for x in input().split()] for _ in range(n)]

n=n0()
a=n1()

ans=0
for i in range(n):
    h=a[i]
    B=list(range(-i,-i+n))
    C=[0]*n
    for j in n:
        C[j]=abs(B[j])-A[j]-h
    ans+=C.count(0)
print(ans//2)

Fixed submission:
def n0():return int(input())
def n1():return [int(x) for x in input().split()]
def n2(n):return [int(input()) for _ in range(n)]
def n3(n):return [[int(x) for x in input().split()] for _ in range(n)]

from collections import defaultdict
n=n0()
a=[0]
a.extend(n1())

m1=[i+a[i] for i in range(n+1)]
m2=[j-a[j] for j in range(n+1)]

d1=defaultdict(list)
d2=defaultdict(list)
for i in range(1,n+1):
    d1[m1[i]].append(i)
    d2[m2[i]].append(i)

ans=0
for i in d1:
    ans+=len(d1[i])*len(d2[i])
            
print(ans)

Buggy python submission (verdict: Runtime Error):
def n0():return int(input())
def n1():return [int(x) for x in input().split()]
def n2(n):return [int(input()) for _ in range(n)]
def n3(n):return [[int(x) for x in input().split()] for _ in range(n)]

import numpy as np
n=n0()
a=n1()
A=np.array(a)

ans=0
for i in range(n):
    h=A[i]
    B=np.array(range(-i,-i+n))
    C=abs(B)-A-h
    ans+=n-np.count_nonzero(C)
print(ans//2)

Fixed submission:
def n0():return int(input())
def n1():return [int(x) for x in input().split()]
def n2(n):return [int(input()) for _ in range(n)]
def n3(n):return [[int(x) for x in input().split()] for _ in range(n)]

from collections import defaultdict
n=n0()
a=[0]
a.extend(n1())

m1=[i+a[i] for i in range(n+1)]
m2=[j-a[j] for j in range(n+1)]

d1=defaultdict(list)
d2=defaultdict(list)
for i in range(1,n+1):
    d1[m1[i]].append(i)
    d2[m2[i]].append(i)

ans=0
for i in d1:
    ans+=len(d1[i])*len(d2[i])
            
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
def n0():return int(input())
def n1():return [int(x) for x in input().split()]
def n2(n):return [int(input()) for _ in range(n)]
def n3(n):return [[int(x) for x in input().split()] for _ in range(n)]

import numpy as np
n=n0()
a=n1()
A=np.array(a)

ans=0
for i in range(n):
    h=A[i]
    B=np.array(range(-i,-i+n))
    C=abs(B)-A-h
    ans+=n-np.count_nonzero(C)
print(ans//2)

Fixed submission:
def n0():return int(input())
def n1():return [int(x) for x in input().split()]
def n2(n):return [int(input()) for _ in range(n)]
def n3(n):return [[int(x) for x in input().split()] for _ in range(n)]

from collections import defaultdict
n=n0()
a=[0]
a.extend(n1())

m1=[i+a[i] for i in range(n+1)]
m2=[j-a[j] for j in range(n+1)]

d1=defaultdict(list)
d2=defaultdict(list)
for i in range(1,n+1):
    d1[m1[i]].append(i)
    d2[m2[i]].append(i)

ans=0
for i in d1:
    ans+=len(d1[i])*len(d2[i])
            
print(ans)