sentences:  For integer "k" ≥ 3, an AP-"k (also called PAP-"k) is any sequence of "k" primes in arithmetic progression.An AP-"k" can be written as "k" primes of the form "a"·"n" + "b", for fixed integers "a" (called the common difference) and "b", and "k" consecutive integer values of "n".An AP-"k" is usually expressed with "n" = 0 to "k" − 1.