Answer
54$\times$ $65^{65534}$ number of variable names possible
Work Step by Step
First digit can be selected in 26 + 26 + 1 + 1 = 54 (uppercase + lowercase + dollar + underscore)
All other digits can be selected in 26 + 26 + 1 + 1 + 10 + 1 = 65
(Uppercase + lowercase + dollar + underscore + numbers + no value)
so total number of variable names = $65^{65534}$$\times$54