The way that you wrote it in your question is just fine.
13.7 billion
137!
137 is in decimal form.
137% written as a fraction in lowest terms is 137/100
137/200 = 0.685
137 million in dollars is $137,000,000
I write 620 billion as 620 billion.
137 written in Roman numerals is CXXXVII
The Colbert Report - 2005 Penn Jillette 2-137 was released on: USA: 1 November 2006
The Colbert Report - 2005 Maira Kalman 6-137 was released on: USA: 28 October 2010
The Colbert Report - 2005 Jonathan Alter 4-137 was released on: USA: 23 October 2008
The Colbert Report - 2005 Lawrence Wilkerson 3-137 was released on: USA: 31 October 2007
The Colbert Report - 2005 Colum McCann 9-137 was released on: USA: 8 August 2013