Chutes and Ladders: on some sequences inspired by 2017 Putnam A1
Abstract
The first problem of the 2017 Putnam competition was to characterize a set of natural numbers closed under both the square-root map n2 n and the "add 5 and square" map n (n+5)2. We reframe this as a problem on an infinite directed graph, using this framing both to generalize the problem and its solution, as well as to determine the first appearance of each number in this set under a row-wise algorithm that outputs all its elements.
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