Insert the missing number 1, 4, 9, 16, 25, 36, 49, (....)
Answer: C
Numbers are 1⊃2;, 2⊃2;, 3⊃2;, 4⊃2;, 5⊃2;, 6⊃2;, 7⊃2;.
So, the next number is 8⊃2; = 64.