The number 23 is the fifth number in the numbers sequence. Below is a list of the appearances of this number in chronological order by episode, and the number 23 in real life.

In Lost:

Season 1:

"Pilot: Part 1"-

• Jack sat in seat 23A.
• Rose sat in seat 23D.
• Bernard sat in seat 23E.

"Tabula Rasa"-

• The award for the capture of Kate was $23,000.

"Solitary"-

• Danielle asks Sayid where Alex is 23 times.

"Homecoming"-

• The song "You All Everybody" is number 234 on the jukebox.

"Deus Ex Machina"-

• One of the crates in the drug smuggler's plane had the number 23 on it.

"Exodus: Part 1"-

• Oceanic Airlines Flight 815 boarded from gate 23.

"Exodus: Part 2"-

• Hurley's hotel room number was 2342.
• The temperature in Sydney on September 22, 2004 was 23C.

Season 2:

"Everybody Hates Hugo"-

• There were 23 survivors in the tail section (which also includes Goodwin).

"The 23rd Psalm"-

• The number is in the name of the title. The 23rd psalm is also known as the "Shepherd's Psalm", which Mr. Eko and Charlie said.

"One of Them"-

• Kelvin Inman showed Sayid part of the video reel #23108-42.
• Sayid was 23 when he was captured in the Gulf War.

"Lockdown"-

• The real Henry Gale's zip code is 55391, which adds up to 23.

"Dave"-

• 23 people were on the deck which was only supposed to hold 8 people when it collapsed.

"Two for the Road"-

• One of the police cars has the number 23 on it.

"3 Minutes"-

• Michael says there are 23 Others (22 at the camp plus Ben at the Swan).

"Live Together, Die Alone"-

• The address on Desmond's unsent letters to Penny was 23 Davismore Gardens (Penny's address).

Season 3:

"A Tale of Two Cities"-

• The time on Jack's pager was 7:15:23.

"Further Instructions"-

• Eddie Colburn's ID number was 84023.

"Every Man for Himself"-

• Munson's $10 million was in unit 23c.

"Not In Portland"-

• Karl was kept in room 23.

"One of Us"-

• Juliet enters the code 1623 in the sonic fence keypad.

"The Man Behind the Curtain"-

• Ben was born 23 miles away from Portland.

"Greatest Hits"-

• The volume on the radio inside the van was at 23 when "You All Everybody" started playing.

Season 4:

"The Economist"-

• Daniel's second clock reads 3:15:23.

"The Constant"-

• The frequency Daniel uses is 2.342.
• Penny lives at 423 Cheyne Walk.
• The Black Rock auction number was 2342.

In Real Life:

• The Average person breaths 23,000 times a day.
• Humans have 23 pairs of chromosomes.
• "The Number 23" was a movie made in 2007 about the number 23.
• There are 23 letters in the Latin alphabet.
• There are 23 official languages in the European Union.