1721

This number is a prime.

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(1721-1)^4 + 1721^4 + (1721+1)^4 = 26317541869937 is prime.

1721 and 1723 are twin primes. Given product of the first 32 primes x = 2*3*...*131, it is curious that x+1721 and x+1723 are also twin primes.

1721 and 1723 are twin primes. The sums of their digits 1+7+2+1 and 1+7+2+3 are also twin primes: 11, 13.

Concatenating the prime previous to 1721 with itself (17091721) is prime. [Noll]

Submitted: 2009-07-02 21:13:59; Last Modified: 2019-01-08 23:30:59.