37777...77773 (36401-digits)

This number is a prime.

+ Let R(n)=(10^n-1)/9. As of December 2003,
34*R(36400)-42000040044444004000024*10^2264*R(36400)/R(4550)-1 was the largest known palindromic prime, all of whose decimal digits are prime. Its formula and proof are described in PrimeForm. [Broadhurst]

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