MathDB
Permutation sequence

Source: 2022 Nigerian MO Round 3/Problem 1

May 2, 2022
Sequencealgebra

Problem Statement

Integer sequence (xn)(x_{n}) is defined as follows; x1=1x_{1} = 1, and for each integer n≥1n \geq 1, xn+1x_{n+1} is equal to the largest number that can be obtained by permutation of the digits of xn+2x_{n}+2. Find the smallest nn for which the decimal representation of xnx_{n} contains exactly 20222022 digits
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