The number 4 is the first number in the numbers sequence. Below is a list of the appearances in chronological order by episode, and the number 4 in real life.

In Lost:

Season 1:

"Pilot: Part 1"-

• The Plane crash was September 22, 2004.
• Jack had 4 scratches on his face.

"Walkabout"-

• Locke was in the wheelchair for 4 years

"White Rabbit"-

• Sawyer made his "birthday wish" 4 years ago.

"The Moth"-

• There are 4 people in the band Drive Shaft.
• Michael said he needs 4 people to help save Jack at the cave-in.

"Confidence Man"-

• Shannon had 4 refiles of inhalers for her asthma.

"Raised By Another"-

• Richard Malkin tried to convince Claire to raise the baby herself for 4 months.

"All the Best Cowboys Have Daddy Issues"-

• Boone's Japanese t-shirt reads the number 84.
• Walt blows on the dice in backgammon 4 times.

"Whatever the Case May Be"-

• There were 4 guns in the marshal's suitcase.

"Hearts and Minds"-

• In Locke's story, he says Michaelangelo stared at the marble for 4 months. Boone replies by saying "We're not going to be staring at the hatch for 4 months?"
• Locke ties up Boone 4 miles away from camp.

"Special"-

• The nurse treating Michael has 4 kids.

"Homecoming"-

• Locke set up 4 traps to capture Ethan.
• When looking for Ethan, Locke says to take a break. Jack replies by saying "I's got to be almost 4 o'clock."

"Outlaws"-

• Hurley says to Sayid that Charlie shot Ethan 4 times (it was actually 6 times).
• The number 4 is on a jersey of a rugby player on TV.

"Numbers"-

• Hurley filled 4 water bottles.
• Hurley's grandfather had a pacemaker put in 4 years ago.
• Leonard Sims was playing Connect 4.
• Sam Toomey died 4 years ago.

"Deus Ex Machina"-

• Boone says "Theresa falls up the stairs, Theresa falls down the stairs" 4 times.
• Locke bangs on the hatch 4 times before the light turns on.

"Do No Harm"-

• Only 4 survivors knew their blood type.
• Sarah is wearing a shirt with the number 44.

"The Greater Good"-

• Essam Tasir was going to use C4 in the suicide bombing.

"Exodus: Part 1"-

• Arzt says the next time the raft can be launched is in 4 months.
• 4 people are on the raft.

"Exodus: Part 2"-

• 4 people went to get the dynamite.
• There were 4 Others on the boat that kidnapped Walt.

Season 2:

"Man of Science, Man of Faith"-

• Kate counts to 4 before asking Locke to stop.

"Adrift"-

• When the countdown reaches to 4 minutes, the alarm sounds, and the code can be entered.

"Abandoned"-

• 4 sticks are needed to build a stretcher for Sawyer.

"The Other 48 Days"-

• Libby says "Donald will be the 4th to go".

"Collision"-

• Only 4 people from the tail section made it.
• Ana-Lucia went back to work 4 months after the shooting.

"What Kate Did"-

• Sam Austen was in Korea 4 months before Kate's birth.

"Maternity Leave"-

• There was 4 planes on the plane mobile.

"Lockdown"-

• Hurley had bet 4 papayas with Sawyer while playing poker.

"S.O.S"-

• Bernard had only 4 people left to help with the sign.

"Two for the Road"-

• Michael shot the gun 4 times.

"?"-

• A system failure occurred September 22 at 4:16 PM.

"Three minutes"-

• There were 4 people on the list.

"Live Together, Die Alone"-

• Libby gives Desmond 4 dollars for coffee.
• There were 4 toes on the statue.

Season 3:

"A Tale of Two Cities"-

• The locker where Kate's clothes were was at 841.

"Further Instructions"-

• Eddie Colburn's ID was 84023.

"Every Man For Himself"-

• Sawyer's prisoner ID was 840.
• Munson's ID was 248.
• A sign at the Hydra reads Area OP-04.

"The Cost Of Living"-

• 4:8:15 is on Mr. Eko's stick.

"I Do"-

• Suzanne has 4 boys.

"Not In Portland"-

• A Drug Juliet gave to Rachel Carlson was called A4993-E3.
• Juliet works in research lab A-4.

"Flashes Before Your Eyes"-

• 4 chimes are heard while Desmond looks at the ring.

"Exposé"-

• Nikki has a role in the 4th season of Exposé.

"Left Behind"-

• Juliet has dislocated her shoulder 4 times.
• Kate's license plate is 40N DNB.
• The gas station in Iowa sold gas for $1.74.
• The Smoke Monster flashed 4 times.

"One of Us"-

• Ben's spine tumor was on his L4 vertebra.

"Greatest Hits"-

• Charlie can hold his breath for 4 minutes.

Season 4:

"The Beginning of the End"-

• There are 4 cars involved in the car chase.
• Hurley Plays Connect 4 with another patient at Santa Rosa.

"Confirmed Dead"-

• There are 4 people from the freighter that arrive on the Island.

"Eggtown"-

• Diane says that for the past 4 years, the doctors have said she has 6 months to live.
• Kate was offered to spend 4 years in prison, which she declines to take.

"The Constant"-

• Penny lives at 423 Cheyne Walk.

In Real Life:

• 4 is a very unlucky number and is associated with death in Asia.
• The central tenets of Buddhism are called the 4 Noble Truths.
• Humans experience life in 4 dimensions: length, width, height, and time.