The "501st Number" refers to the 501st term in a sequence or series of numbers. In mathematics, sequences can be arithmetic, geometric, or follow other specific patterns. The 501st number can be calculated based on the rules governing the particular sequence being analyzed. For example, in the case of the natural numbers, the 501st number is simply 501. In other sequences, such as the Fibonacci sequence, the 501st number would be determined by adding the two preceding numbers in the series. Understanding the context of the sequence is essential for identifying the 501st number accurately.