The following numbers represent values of the dependent variable that corresponds to equally spaced values of the independent variable. Classify these sequences as linear, exponential or neither:

sequence	classification
1, 2, 4, 8, 16, ...
-3, -6, -9, -12, -15, ...
-1, 0, 2, 5, 9, ...
1, 4, 9, 16, 25, ...
1, 4, 16, 64, 256, ...
10, 15, 20, 25, 30, ...