11111...11111 (30-digits)

This number is a prime.

1111111111 1111281111 1111111111

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Inserting "n" in the middle of n 1's (n = 28) is the largest prime of this type less than a googol. [Marcel]

Submitted: 2026-01-28 05:00:06; Last Modified: 2026-01-28 13:01:15.