I write 620 billion as 620 billion.
Sixteen point two billion is how I would write it.
You write 3.56 billion as 3,560,000,000.
You can write 40.3 billion as 40,300,000,000.
You can write out 1.8 billion as "1,800,000,000" or "one billion eight hundred million."
621,428,512,953
three billion twelve million four hundred twenty-eight thousand
I write 620 billion as 620 billion.
Sixteen point two billion is how I would write it.
You write 3.56 billion as 3,560,000,000.
400 400 and a 428 400 and a 428 400 and a 428 400 and a 428 400 and a 428 400 and a 428 400 and a 428 400 and a 428 400 and a 428 400 and a 428 400 and a 428 400 and a 428 400 and a 428 400 and a 428 400 and a 428 400 and a 428 400 and a 428 400 and a 428 400 and a 428 400 and 428
You can write 40.3 billion as 40,300,000,000.
You can write out 1.8 billion as "1,800,000,000" or "one billion eight hundred million."
428 is an integer and not a fraction. However, it can be expressed in rational form as 428/1. That is the simplest form. There is no sensible way of writing it as a mixed number.
Since you asked how I would write the number, the answer is 1031.
1,000 billion billion is: 1,000,000,000,000,000,000,000
four hundred twenty eight = 428