Question

first five terms of an=an-1+6

Answer 1

Your series is a recursive one. This means that to know the nth term you need to know the vale of the (n-1)th term. Thus to know the second term you need to know the first term. Is the value of the first term given in the question?

Answer 2

as an aside to terminology.

a sequence is a list of elements, either random or generated: listing terms define a sequence. a1, a2, a3, a4, a5

a series is the sum of the terms in a list ... a1 + a2 + a3 + a4 + a5

a sequence of partial sums kinda blends the 2 concepts

s1 = a1
s2 = a1 + a2
s3 = a1 + a2 + a3
etc ...

Answer 3

but as is, you can still list the terms, you just have to leave a1 variable