Answer
A.P. with common difference $4$ and initial term $1$.
Work Step by Step
Since,we have $a_n=4n-3$
Thus, $a_1=1,a_2=5,a_3=9,a_4=13,a_5=17$
$a_2-a_1=5-1=4$;
$a_3-a_2=9-5=4$;
$a_4-a_3=13-9=4$
and
$a_5-a_4=17-13=4$
Hence, we can conclude that this is an A.P. with common difference $4$ and initial term $1$.
