Two patterns alternate here. The first pattern begins with 10 and adds 2 to each number to arrive at the next; the alternating pattern begins with 34 and subtracts 3 each time.
Here, every other number follows a different pattern. In the first series, 6 is added to each number to arrive at the next. In the second series, 10 is added to each number to arrive at the next.
In this alternating repetition series, the random number 21 is interpolated every other number into an otherwise simple addition series that increases by 2, beginning with the number 9.
EXAMIANS