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Some, though not all, of the Sumerian numbers are known from syllabic spellings. There is an overview here alt link
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Sumerian has been a dead language for nearly 4,000 years, and had no known linguistic descendants, predecessors, or relatives.
Its printed form was logographic, which means each word was represented by a symbol. So there's no phonological content to be gleaned from their writing either.
So we don't know for sure how any of it was pronounced.