Question

Select the first five terms in the arithmetic sequence (a) drop (n) =8n

Answer 1

You may be trying hard to make something difficult out of something easy here.

You have said that  a(n) = 8n .  (I can't write a subscript 'n'on this site either,
but  'a(n)'  will serve the same purpose.) 

So . . . (get ready) . . .

a(n) = (8) times (n)
a(1) = 8
a(2) = 16
a(3) = 24
a(4) = 32
a(5) = 40
a(6) = 48
.
.
a(100) = 800
a(101) = 808
.
.
etc.