Final answer:
The correct formula for an arithmetic sequence is an = a1 + (n - 1)d (option 1), which gives the value of the nth term by adding the common difference to the first term (n - 1) times.
Step-by-step explanation:
The formula for an arithmetic sequence is represented by option 1, which is an = a1 + (n - 1)d. Here, an represents the nth term of the sequence, a1 is the first term, n is the term number, and d is the common difference between terms. This formula gives the value of any term in an arithmetic sequence by starting at the first term and adding the common difference d repeatedly (n - 1) times.