How largest the definite number?
Googol: The larger number, '1' followed by one hundred zeros $(i.e \;10^{100})$, which is shown as follows:
$googol\;=\;10^{100}\;=\;$10,000,000,000,000,000,000,000,000,000,000, 000,000,000,000,
000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,
000,000,000,000
A googol is larger than the number of elementary particles in the universe, which amount to only $10$ to the $80^{th}$ power.
Googolplex: The second largest number. A '1' followed by a googol of zeros. Which can be written as:
$googolplex\; = \; 10^{googol}\; = \; 10^{(10^{100})}$
This first volume contains the initial digit one with which googolplex start:
Googolplexian: The world's largest number. A '1' followed by a googolplex of zeros.