Answer
$12,338,352$
Work Step by Step
$n$ objects in $r$ spots where each spot can contain any of the objects is $n^r$.
Thus, the number of $4$-letter long company names is $26^4=456976$.
The number of $5$-letter long company names is $26^5=11881376$
Hence, the total number of possible company names is:
$456976+11881376=12338352$
