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An easy problem about a sequence

Source: 2023 China South-east Mathematics Olympiad Grade 10 P1

July 31, 2023
algebraSequence

Problem Statement

The positive sequence {an}\{a_n\} satisfies:a1=1a_1=1 and an=2+an121+an1(n2)a_n=2+\sqrt{a_{n-1}}-2 \sqrt{1+\sqrt{a_{n-1}}}(n\geq 2) Let Sn=k=1n2kakS_n=\sum\limits_{k=1}^{n}{2^ka_k}. Find the value of S2023S_{2023}.