13. (9+17)/2=13
13
Average = 13
1 5 9 13 17 21
5, 13 and 17 are prime.
You average the two numbers in the middle. For example, if you have the numbers 9, 13, 17, and 20, the median is the average of 13 and 17, which is 15.
Between 9 and 17. 9 being very early and 17 being very late. 13 is the average.
13 + 9 + 17 = 39
9, 11, 13, 15, 17, 19, 21
It is 4n+5 and so the next term will be 25
Add them together and divide by 6.
Mean is the same as average