158

This number is a composite.

The sum of the first nine Mersenne prime exponents. [Russ]

The smallest number such that the sum of the number and its reverse is a prime that is not palindromic, i.e., 158 + 851 = 1009. [Gupta]

Inserting 158 zeros between the first four consecutive primes results in a prime, 2*10^(3*159)+3*10^(2*159)+5*10^159+7. [Opao]

75*158^75+1 and 76*158^76+1 are both prime. However, neither 75*a^75+1 nor 76*a^76+1 are prime for any smaller a! [Hartley]