Streak · 7 days+185 XP
7-Day O-Word Streak
Learn one new word that starts with O each day and use it in a sentence. Check in once a day.
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Language · Facts & stats · iChallenge network
The O Challenge
Daily facts and stats about the letter O, plus real challenges to put them to work.
Warm-up questionNot ranked · tap an answer
In Big O notation, what does O(n) describe?
O(n) means linear growth: double the input and the work roughly doubles.
Level1Rookie
XPPlay a round to earn XP
Streak0days
LeagueBronzeweekly
Daily #8Resets at midnight UTC
Today's round
- 5 questions
- 20s each
- 0 played today
One ranked attempt per day. Practice as much as you like.
Challenges
Join one, log your days or post your proof. Finishing earns XP and the Finisher badge.
Proof+250 XP
Circle Hunt
Find and photograph five O-shaped circles around your home or street, then post the photos or a short list.
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Streak · 10 days+200 XP
10-Day Phonetic Alphabet Streak
Learn a few letters of the NATO phonetic alphabet each day, starting with Oscar, until you know all 26. Check in daily.
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By the numbers
Live counts from OChallenge.com. All arena stats →
Facts in the pack12
Visitors, 30 days59
Leaderboard
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Badges
Earned on any arena, shown on your profile everywhere.
First RoundFinish your first daily round.
FlawlessAnswer every question in a round correctly.
LightningA perfect round in under 25 seconds.
On a RollPlay 3 days in a row.
Week WarriorPlay 7 days in a row.
UnbreakablePlay 30 days in a row.
ExplorerPlay daily rounds in 5 different arenas.
GlobetrotterPlay daily rounds in 25 different arenas.
PolymathPlay daily rounds in 5 different topics.
In the ArenaJoin your first challenge.
FinisherComplete a challenge.
RecruiterInvite a friend who finishes a round.
CaptainInvite 5 friends who finish a round.
PodiumFinish a day in an arena's top 3.
ChallengerReach level 10.
Profile SavedSave your progress with an email.
Save your progress
Add your email to keep your level, streak and badges if you switch devices, and carry them to every iChallenge arena. One email when you save; no spam.
Put a prize on a challenge
Fund a prize on OChallenge.com and your brand sits on the challenge card, the leaderboard and every finisher's share. Prizes only appear once they're funded, so players can trust what they see.
- Pick the challenge and the prize
- We review entries before a funded prize is awarded
- You get finisher and engagement numbers after it closes
Current sponsors
Questions
How do I start?
Play today's quiz round, post your score, and start a streak.
What do I earn?
XP, levels, streaks and badges. Save your progress with an email and it follows you to every arena on the iChallenge network.
How does the daily round work?
Everyone on this arena gets the same five questions each day, from easy to hard. You get one ranked attempt; practice rounds are unlimited.
How is my score calculated?
100 points per correct answer, up to 50 more for answering quickly, a combo multiplier for answers in a row, and 150 bonus points for a perfect round.
Is it free?
Yes. Playing, streaks, badges and leaderboards are free. Some challenges carry a sponsor-funded prize; the challenge card shows it when one is funded.