Stack Exchange network consists of 183 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.
Here is its numerical solution for required values of parameters done with Maple:
a := .22: n := 5: mu := 3.18: fsolve(a = add(exp(-mu)*((mu-mu2)/mu2)^k*BesselI^(k/2)*BesselI(k, 2*sqrt((mu-mu2)*mu2)), k = 1 .. n));
$1.835791770 $$2.002275629 $
a := .22: n := 5: mu := 3.18: fsolve(a = add(exp(-mu)*((mu-mu2)/mu2)^k*BesselI(k, 2*sqrt((mu-mu2)*mu2)), k = 1 .. n));
$1.835791770 $
a := .22: n := 5: mu := 3.18: fsolve(a = add(exp(-mu)*((mu-mu2)/mu2)^(k/2)*BesselI(k, 2*sqrt((mu-mu2)*mu2)), k = 1 .. n));
$2.002275629 $