Value k

When discussing Mersenne numbers, all factors can be expressed in the following form:

[math]\displaystyle{ 2kp+1 }[/math] where [math]\displaystyle{ p }[/math] is the exponent in [math]\displaystyle{ 2^p-1 }[/math].

An example:

[math]\displaystyle{ 2^{23}-1 = 8388607 = 47 * 178481 }[/math]

[math]\displaystyle{ 47 = 2 * 1 * 23 + 1 }[/math]

[math]\displaystyle{ 178481 = 2 * 3880 * 23 + 1 }[/math]

So, we see that for the factor 47, [math]\displaystyle{ k=1 }[/math] and for 178481, [math]\displaystyle{ k=3880 }[/math].

When trial factoring finds a factor, it can either be written out and stored long hand, or just the k-value may be recorded.

See also: http://www.mersenne.org/various/math.php