public function dataProviderForCubicNumber() { return [[-1, []], [0, []], [1, [0]], [2, [0, 1]], [3, [0, 1, 8]], [20, [0, 1, 8, 27, 64, 125, 216, 343, 512, 729, 1000, 1331, 1728, 2197, 2744, 3375, 4096, 4913, 5832, 6859]]]; }