11111...11111 (441-digits)
This number is a prime.
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As of February 12, 2026, this is the largest "perimeter prime", i.e., a square-congruent prime such that the interior digits are all exactly the same. [Reamy]
Submitted: 2026-02-12 18:00:19; Last Modified: 2026-10-31 12:31:22.
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