Originally Posted by sweety439
This divisor is always gcd(k+1,b1) (+ for Sierpinski,  for Riesel), e.g. for R7, k=197, the divisor is gcd(1971,71) = 2, and for S10, k=269, the divisor is gcd(269+1,101) = 9. Besides, for SR3, the divisor of all even k is 1 and the divisor of all odd k is 2.
Thus, for example, for R13, the divisor of k=1, 2, 3, ... are {12, 1, 2, 3, 4, 1, 6, 1, 4, 3, 2, 1, 12, 1, 2, 3, 4, 1, ...}, and for S11, the divisor of k=1, 2, 3, ... are {2, 1, 2, 5, 2, 1, 2, 1, 10, 1, 2, 1, 2, 5, 2, 1, 2, 1, ...}.
