9 12 11 14 13 16 15

This is an alternating repetition series, in which a random number, 61, is interpolated as every third number into an otherwise simple subtraction series. Starting with the second number, 57, each number (except 61) is 7 less than the previous number.

This is a simple subtraction with repetition series. It begins with 20, which is repeated, then 3 is subtracted, resulting in 17, which is repeated, and so on.

In this simple subtraction series, each number is 6 less than the previous number.

In this simple addition series, each number is 5 greater than the previous number.

In this simple addition series, each number is 5 more than the previous number.

This is an alternating repetition series, with a random number, 22, interpolated as every third number into an otherwise simple addition series. In the addition series, 4 is added to each number to arrive at the next number.

This is a subtraction series with repetition. Each number repeats itself and then decreases by 9.

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.

This is an alternating addition series, in which 10 is added, then 5, then 10, and so on.

This is an alternating subtraction series in which 2 is subtracted twice, then 3 is subtracted once, then 2 is subtracted twice, and so on.