is x 0 y 1 x 1 y 3 x 2 y 9 x 3 y 27 x 4 y 81

a nonlinear function
nonlinear not function
linear function
linear not a function

This sequence represents a nonlinear function. Each x-value (0, 1, 2, 3, 4) is being raised to the power of 3 to get the corresponding y-value (1, 3, 9, 27, 81), which is not a linear relationship.