Answer: the previous number multiplied by four and added to one.
Explanation: a pattern is a particular way in which something is done, is organized, or happens, it is also something that is repeated. A number pattern is a list of numbers that follows certain rules or sequence. In the given list, we can see that each number is the previous one multiplied by four and added to one:
(5*4)+1=21
(21*4)+1=85
(85*4)+1=341
