21,42,126,504 If it is a geometric sequence, choose the common ratio. If it is not a geometric sequence, choose "not geometric.

Not geometric

Step-by-step explanation:

In a geometric sequence, each term is multiplied by a common ratio to get the next term.

So if this is a geometric sequence, then dividing each term by the one before it should result in the same common ratio.

42 / 21 = 2

126 / 42 = 3

504 / 126 = 4

The ratios are different. This is not a geometric sequence.