Find the invalid no.from the following series 15, 16, 34, 105, 424…

Find the invalid no.from the following series 15, 16, 34, 105, 424, 2123, 12756

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 #8124

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