R:  number of primes in the input
c1:  number of times merge was called
c2:  number of times a < comparison was executed in merge
c3:  time factor predicted by formula
r1:  c1/c3
r2:  c2/c3

R    c1    c2    c3   r1    r2
 2  2002  3002  1667 1.201 1.801
 3  3276  5095  4133 0.793 1.233
 4  4227  6821  7057 0.599 0.967
 5  4989  8203 10137 0.492 0.809
 6  5673  9534 13440 0.422 0.709
 7  6303 10744 16834 0.374 0.638
 8  6921 11966 20377 0.340 0.587
 9  7499 13098 23983 0.313 0.546
10  8015 14108 27602 0.290 0.511
11  8538 15149 31314 0.273 0.484
12  9025 16107 35040 0.258 0.460