Complete the number series: 1, 8, 4, 27, 9, ______?

None of these

The pattern of the series is:

1³ = 1, 2² = 4, 2³ = 8, 3² = 9, 3³ = 27

Following this pattern:

4² = 16 (skipped), 4³ = 64

So, the next number in the series is 64.