Look at this series: 5, 61, 213, 509 ....... What number should come next?

This series appears to be a cubic series. The pattern seems to be that each number is the cube of a natural number plus 4.

Let's break it down:

• 5 is 1 cubed (1) plus 4.
• 61 is 4 cubed (64) minus 3.
• 213 is 6 cubed (216) minus 3.
• 509 is 8 cubed (512) minus 3.

So, the pattern is that we're cubing every second natural number (1, 4, 6, 8), and then subtracting 3 from the result.

The next natural number in this sequence would be 10.

So, the next number in the series would be 10 cubed (1000) minus 3, which equals 997.