This is a scientific way of writing a very large number. It is only accurate to 17 significant figures, which means we don’t know the entire number accurately. To write it out completely it would be rounded up to 17 figures and look like:
121305393447191570000000000000 or:
121,305,393,447,191,570,000,000,000,000.
There are 29 digits after the leading digit, 1.
The actual whole number could be about 5,000,000,000,000 (5 trillion) less or more than this.
So it would be impossible to tell whether it is a prime number, or whether it factorises.