Look at this series: 2, 1, 4, 2, 18....... What number should come next?12152129

This series is a bit tricky because it doesn't follow a simple arithmetic or geometric progression. However, if you look closely, you can see that the pattern is as follows:

• The first number is 2.
• The second number is 1, which is half of 2.
• The third number is 4, which is 2 squared.
• The fourth number is 2, which is the square root of 4.
• The fifth number is 18, which is 2 times the fourth number (2) to the power of 3.

Following this pattern, the next number should be the fifth number (18) divided by 2, which is 9.