Answer = the
According to the pattern he started with
The first term = 1
The common difference = 4
The nth term of a Arithmetic sequence =
Tn = a + (n - 1) d
Where a = first term , d = common difference, n = number of terms
a = 1, d = 4, and n = 15
T15 = 1 + (15 - 1) x 4
T15 = 1 + ( 14) x 4
T15 = 1 + 56
T 15 = 57