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.
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 write 3.56 billion as 3,560,000,000.
You can write 40.3 billion as 40,300,000,000.
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.
You can write out 1.8 billion as "1,800,000,000" or "one billion eight hundred million."
Since you asked how I would write the number, the answer is 1031.
four hundred twenty eight = 428
1,000 billion billion is: 1,000,000,000,000,000,000,000