IQ Test · Adults Question 16

What number should replace the question mark? Six circles contain: 1, 5, 7, 9, 2, 3, 6; 8, 7, 6, 3, 2, 7; 6, 7, 3, 2, 9, 6; 7, 5, 9, 1, 6, 2, 3; 1, 6, 2, 2, 5, 9, 8; 1, 9, ?, 4, 8, 7, 2. Answer with a natural number.