# 4

This number is a composite.

Just showing those entries submitted by 'Silva': (Click here to show all)

There are 4 two-digit primes formed by concatenation of prime digits. [Silva]

4 is the smallest number between twin primes. [Silva]

The only semiprime expressed by a prime p in two ways: p^2 and p+p. [Silva]

The number of 4-digit primes formed from the first 4 odd digits. [Silva]

4!!-3!!+2!!-1!! is a 4!-digit prime. [Silva]

4 is the number of primes formed from 4 digits summing up to 4 [Silva]

The only digit that forms a prime with the previous digit (43). [Silva]

4 is the number of 4-digit primes formed from the first 4 natural numbers: 1423, 2143, 2341, 4231. [Silva]

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

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