A prime is called left-truncatable (or just truncatable) if deleting any string of digits from its left always leaves behind another prime. For example, 317 is a left-truncatable prime because both 17 and 7 are also prime. To exclude trivial cases, the digit zero must not appear in the original number.

The largest left-truncatable prime in base 10 is 357686312646216567629137.

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