A Generalized Repunit Conjecture:
For any base b, which has prime numbers of the form Rb[n]=(b^p-1)/(b-1) 
,the prime numbers will be distributed near the best fit line

Y = G * logb(logb(Rb[n])) + C

,where limit n-> Inf, G = 1/e^gamma = 0.56145948...
gamma is Euler's constant.
logb  is the logarithm in base |b|.
Rb[n] is the nth sequential repunit prime number in base b.
C     is a data fit constant which varies with b.

Generalizing the Wagstaff Mersenne Conjecture and the work of Pomerance 
and Lenstra, as outlined by Caldwell at

http://primes.utm.edu/mersenne/heuristic.html

,we also have the following 3 properties:

1. The number of Repunit primes less than or equal to x is about       
   e^gamma * logb logb x.

2. The expected number of Repunit primes (b^p-1)/(b-1) with p between x 
   and |b|x is about e^gamma. 

3. The probability that (b^p-1)/(b-1) is prime is about
   e^gamma / (p log |b|).

For negative bases, p can not be 2, and the summation in 1 is closer to 
e^gamma * logb(logb(x)/3), which will converge slowly.  For practical 
exponents, p < 1e6, G ~ 0.47.

The current linear data fits for the first few bases are listed below:

b     #primes     G          C     largest known exponent
-12      9      .48686   +.26244        24071
-11      7      .47650   +.17286        6113
-10     10      .33115   +.15048        3011
-9       9      .43930   +.66336        49223
-7       9      .63511   -.51818        106187
-6      14      .44014   +.14829        41341
-5      11      .65828   +.51129        193939
-3      23      .45540   +.86304        152287
-2      40      .47271   +.65033        986191

 2      47      .55715   +.92757        43112609
 3      16      .62162   +1.0636        57917
 5      16      .43711   +.08611        201359
 6      14      .46809   -.24593        79987
 7       8      .78784   -.14225        126037
10       9      .70637   -.39537        270343
11      11      .31087   +.90528        20161
12      13      .37669   -.39149        46889
13      11      .31876   +.56306        31751
14       9      .55408   -.56477        67421