1, 3, 9, 27, ... Arithmetic, common difference is 5

It is not arithmetic.

See below.

Step-by-step explanation:

1 3 9 27 is not an arithmetic function because the terms do not increment by a constant amount.

3 - 1 = 2, 9 - 3 = 8

and 27 - 9 = 18,

It is a geometric function with common ratio 3.