Which of the following is a recursive formula for the sequence 1,2,3,4,…1, 2, 3, 4, \dots1,2,3,4,…?
an=an−1+1a_n = a_{n-1} + 1an=an−1+1, a1=1a_1=1a1=1
an=2an−1a_n = 2a_{n-1}an=2an−1, a1=1a_1=1a1=1
an=n⋅an−1a_n = n \cdot a_{n-1}an=n⋅an−1, a1=1a_1=1a1=1
an=an−1−1a_n = a_{n-1} - 1an=an−1−1, a1=1a_1=1a1=1