This sequence alternates between cubes of odd numbers and squares of even numbers: 1^3 = 1, 2^2 = 4, 3^3 = 27, 4^2 = 16, 5^3 = 125 (which is Z), 6^2 = 36, 7^3 = 343. The pattern is clear: odd positions are cubes (1, 3, 5, 7) and even positions are squares (2, 4, 6).