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Alternate deletion around a circle of 2000

Question

The integers 11 to 20002000 are written clockwise around a circle. Going clockwise from 11, you remove a number, spare the next, remove the next, spare the next, and so on until you have passed every remaining number once. Each new pass starts again at the smallest remaining number, which is removed, with removing and sparing alternating as before. Which number is the very last to be removed?

Short answer

10241024. Each pass keeps only the numbers in even positions of the current list, so after pass kk the survivors are multiples of 2k2^k (odd-length passes simply remove the final element too). The process ends with the largest power of 22 not exceeding 20002000, namely 10241024.

Adapted from QuantQuestions.io; question and answer rewritten by SelfMadeQuant.com.

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