Count of pairs in given Array with product of their values equal to sum of their indices (arr[i]*arr[j] = i+j)

# Python3 program for the above approach

# Function to find the number of
# unique pairs
def NumberOfRequiredPairs(arr, N) :

	# Variable that with stores
	# number of valid pairs
	ans = 0;

	# Traverse the array for every
	# possible index i
	for i in range(N) :

		# Initialize a dummy variable
		# for arr[i]
		k = arr[i];

		# We will loop through every
		# multiple of arr[i];
		# Looping through 2*N because
		# the maximum element
		# in array can be 2*N
		# Please not that i and j are
		# in 1 based indexing
		while (k <= 2 * N) :

			# Calculating j
			j = k - i - 1;

			# Now check if this j lies
			# between the bounds
			# of the array
			if (j >= 1 and j <= N) :

				# Checking the required
				# condition
				if ((arr[j - 1] == k // arr[i]) and j > i + 1) :
					ans += 1;

			# Increasing k to its next multiple
			k += arr[i];

	# Return the ans
	return ans;

# Driver Code
if __name__ == "__main__" :

	# Given Input
	N = 5;
	arr = [ 3, 1, 5, 9, 2 ];

	# Function Call
	print(NumberOfRequiredPairs(arr, N));