 The interesting property of this series is that for each concept \( C_k\), all and only the numbers of the concepts preceding \(C_k\) in the sequence fall under \(C_k\). So, for example, the concepts preceding \(C_3\) are \(C_0\), \(C_1\), and \( C_2\). Accordingly, all and only the following numbers fall under \( C_3:\#C_0, \#C_1\), and \(\#C_2\).