Here is the bifurcation parameter, is the variable. The values of for which the period doubles (e.g. the largest value for with no orbit, or the largest with no orbit), are , etc. These are tabulated below:Alligood, p. 503.
Here is the bifurcation parameter is the variable The values of for which the period doubles (eg the largest value for with no orbit or the largest with no orbit) are  etc These are tabulated belowAlligood p 503