This is something of an extension of this question which is currently unanswered. I've done some rearranging of my initial equation which was originally:
$$ \frac{M_t}{M_\infty} = 1 - \frac{32}{\pi} * \sum_{n=1}^{25}\frac{exp(-q^2_nDt/R^2)}{q_n^2} * \sum_{p=0}^{100} \frac{exp(-(2p+1)^2)\pi^2Dt/H^2)}{(2p+1)^2} $$
and simplified it to perhaps make it easier to answer. My equation is now:
$$ A = \sum_{n=1}^{25}\sum_{p=0}^{100}\frac{(E_nG_p)^D}{F_nI_p} $$
I am trying to solve for D; all other values are known. I'm just a bit stumped on how to isolate D.
Update: Here are some examples of data used in the original equation.
$\frac{M_t}{M_\infty}$ = 0.663228201
$t$ = 1123000
$H$ = 0.003235088
$R$ = 0.001268375
$D$ = 1.13816081338369290421042023809E-13
$q_1$ = 2.404825557695772768621631879326454643124244909145967135706
$q_2$ = 5.520078110286310649596604112813027425221865478782909853757