1579

This number is a prime.

The hull number of Cape Keltic in the Hallmark Hall of Fame movie Calm at Sunset. [Haga]

The mouth of a "prime volcano." It is the smallest prime that remains prime when preceded and followed by one, two, three, or four 9's:

     1579 
    915799 
   99157999 
  9991579999
 999915799999

The largest prime that consists of odd digits concatenated in ascending order. [Loungrides]

The smallest 4-digit prime, with distinct digits, whose alternating the two internal digits another prime is created, (1759), concatenated from two double-digit primes. [Loungrides]

The sum of the squares of the first eight semiprimes is 1579. Note that the eighth semiprime is 1+5+7+9. [Worrom]