Answer
Arithmetic sequence and the common difference is $ d=1$.
Work Step by Step
We are given that $ a_n=n+5$
Here, we have the first four terms:
$ a_1=6, a_2=7,a_3=8,a_4=9$ when $ n=1,2,3,4$
Now, subtract each two consecutive terms:
$ a_2-a_1=7-6=1; a_3=a_2=8-7=1; a_4-a_3=9-8=1$
We can see that this is an arithmetic sequence and the common difference is $ d=1$.
