Find the missing number?

[amp_mcq option1=”9″ option2=”6″ option3=”3″ option4=”13″ correct=”option1″]

The missing number is $\boxed{3}$.

The sequence is $1, 4, 9, 16, 25, 36, \boxed{49}, 64, 81$. It is a sequence of squares of natural numbers.