The Tonight Show
Hosting history

Host
Start date
End date
Episodes
Steve Allen
September 27, 1954
January 25, 1957
2,000
Ernie Kovacs
October 1, 1956
January 22, 1957
2,000
Jack Lescoulie
January 28, 1957
June 21, 1957
2,000
Al "Jazzbo" Collins
June 24, 1957
July 26, 1957
2,000
Jack Paar
July 29, 1957
March 30, 1962
2,000
Various hosts
April 2, 1962
September 28, 1962
2,000
Johnny Carson
October 1, 1962
May 22, 1992
4,531
Jay Leno (first tenure)
May 25, 1992
May 29, 2009
3,775
Conan O'Brien
June 1, 2009
January 22, 2010
146
Jay Leno (second tenure)
March 1, 2010
February 6, 2014
835
Jimmy Fallon
February 17, 2014
present
1,059

Question: How many episode did O'Brien host before Leo was brought back as host ?
Answer: O'Brien hosted 146 episodes over the course of less than eight months before Leno was brought back as host, where he served for almost four additional years.