The given sequence of numbers is 3, 4, 9. The pattern in the sequence is not immediately clear, as there are no obvious mathematical operations or patterns between the numbers. However, upon closer inspection, it can be observed that each number in the sequence is one less than a perfect square. 3 is one less than 4 (2^2), 4 is one less than 5 (3^2), and 9 is one less than 10 (4^2). Therefore, the 2nd number in the sequence is 4.