The nth term in an arithmetic sequence is given by n = a + (n - 1) * d, where a is the first term in the sequence, and d is the common difference, given by the expression 2nd term - 1st term = 3rd term - 2nd term = nth term - (n - 1)th term.
So,
n = 1 + (n - 1) * (7 - 1)
n = 1 + (n - 1) * 6
n = 1 + 6n - 6
Take like terms,
n - 6n = 1 - 6
-5n = -5
n = 1,
So the nth term is equal to 1