An arithmetic sequence (sometimes called a “progression”) is a particular type of sequence that has an initial value, as with all sequences. A proper arithmetic sequence has a common difference, that when added to the initial number and each consecutive number, provides the arithmetic sequence. An arithmetic sequence may begin with a negative number as long as the sequence increases from that value. Arithmetic sequences are non-random, yielding a method for their continuation.

An arithmetic sequence example would look like this:

1, 5, 9, 13, 17, 21, 25, 29, … with a common difference of 4.

Look for the common difference by subtracting the preceding value from the current value and ensuring this holds for the following numbers.

### Instructions

**1.**

Is this sequence an arithmetic sequence? 2, 1, 3, 4, 7, 11, ….

Assign `"yes"`

or `"no"`

to `checkpoint_1`

.

**2.**

If we have 1, 4, 7, 10, 13, 16, 19, 22, 25, …, what is the number following “25?”

Assign the answer to `checkpoint_2`

.