What is the sum of this series

What is the sum of this series? 1, 3, 5, 7, 9, ...... 77.

This problem repeats another one in the library (at most with different numbers), so it's left out of browsing.

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AQuA-RAT — Algebra Question Answering with Rationales (Ling et al., DeepMind, 2017) · train #37070

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