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MathNet 2018-part-04 — 181 problems (EN–VI) Question 29

Math Olympiad Vault · MathNet 2018-part-04 — 181 problems (EN–VI)

Question 29

Suppose that $\{a_{n}\}_{n \geq 1}$ is an arithmetic sequence of real numbers such that
$$
\begin{array}{r}
a_{1}+a_{2}+a_{3}+a_{4}+\cdots+a_{10}=20 \\
a_{1}+a_{4}+a_{9}+a_{16}+\cdots+a_{100}=18
\end{array}
$$
Compute $a_{1}+a_{8}+a_{27}+a_{64}+\cdots+a_{1000}$.