Here is a more than 6,532,490 digit near rational approximation involving the MRB constant.
If is rational then is a quadratic.
It seems that one can make arbitrarily close rational approximations for c,n in involving the MRB constant (MB), as well as many other constants. The location of a given constant on the number line will enable c and n to be smaller and still produce an approximation that is accurate to several digits. MB is in a spot that is very efficient at yielding approximations to several digits of accuracy for many given n's with c=17/8. as shown by a nearly flat line region of the MinkowskiQuestionMark function: