We study a class of integers called SP numbers (Sum Prime numbers). An SP number is by denition a positive integer d that gives rise to a prime number (a + b)=gcd(4; 1 + d) from every factorization d = ab. We also discuss properties of SP numbers in relations with arithmetic of imaginary quadratic elds (least split primes, exponents of ideal class groups). Further we point out that special cases of SP numbers provide the problems of distribution of prime numbers (twin primes, Sophi-Germain primes, quadratic progressions). Finally, we consider the problem whether there exist innitely many SP numbers.

Mathematics Subject Classication. Primary 11A41;Secondary 11R11,11R29