# 80

This number is a composite.

There are 80 four-digit primes which are concatenations of two-digit primes. [De Geest]

(10^{80} - 80)/80 is prime.
[Luhn]

80^(80+1) + (80+1)^80 is prime.

The largest natural number n such that all prime factors of n and n+1 are smaller or equal to the prime digit 5. [Capelle]

The only two-digit integer *n* that yields a prime in the
form *n*^(*n*+1)+(*n*+1)^*n*. [Silva]

The smallest integer n such that both n and n+1 are products of at least 4 primes. [Post]

Theoretically, the fewest prime factors in the numbers spanning a non-trivial 8-tuple. [Merickel]

(There is one curio for this number that has not yet been approved by an editor.)

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