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True Random Number Service

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What’s this fuss about true randomness?

Perhaps you have wondered how predictable machines like computers can generate randomness. In reality, most random numbers used in computer programs are pseudo-random, which means they are generated in a predictable fashion using a mathematical formula. This is fine for many purposes, but it may not be random in the way you expect if you’re used to dice rolls and lottery drawings.

RANDOM.ORG offers true random numbers to anyone on the Internet. The randomness comes from atmospheric noise, which for many purposes is better than the pseudo-random number algorithms typically used in computer programs. People use RANDOM.ORG for holding drawings, lotteries and sweepstakes, to drive online games, for scientific applications and for art and music. The service has existed since 1998 and was built by Dr Mads Haahr of the School of Computer Science and Statistics at Trinity College, Dublin in Ireland. Today, RANDOM.ORG is operated by Randomness and Integrity Services Ltd.

Games and Lotteries

Lottery Quick Pick is perhaps the Internet’s most popular with over 280 lotteries
Keno Quick Pick for the popular game played in many countries
Coin Flipper will give you heads or tails in many currencies
Dice Roller does exactly what it says on the tin
Playing Card Shuffler will draw cards from multiple shuffled decks
Birdie Fund Generator will create birdie holes for golf courses

Random Drawings

Q3.1 in the FAQ explains how to pick a winner for your giveaway for FREE
Third-Party Draw Service is the premier solution to holding random drawings online
Step by Step Guide explains how to hold a drawing with the Third-Party Draw Service
Step by Step Video shows how to hold a drawing with the Third-Party Draw Service
Price Calculator tells exactly how much your drawing will cost
Drawing FAQ answers common questions about holding drawings
Public Records shows all completed drawings going back five years
Drawing Result Widget can be used to publish your winners on your web page
Multi-Round Giveaway Service for verified video giveaways


Integer Generator makes random numbers in configurable intervals
Sequence Generator will randomize an integer sequence of your choice
Integer Set Generator makes sets of non-repeating integers
Gaussian Generator makes random numbers to fit a normal distribution
Decimal Fraction Generator makes numbers in the [0,1] range with configurable decimal places
Raw Random Bytes are useful for many cryptographic purposes

Lists and Strings and Maps, Oh My!

List Randomizer will randomize a list of anything you have (names, phone numbers, etc.)
String Generator makes random alphanumeric strings
Password Generator makes secure passwords for your Wi-Fi or that extra Gmail account
Clock Time Generator will pick random times of the day
Calendar Date Generator will pick random days across nearly three and a half millennia
Geographic Coordinate Generator will pick a random spot on our planet’s surface
Bitmaps in black and white
Hexadecimal Color Code Generator will pick color codes, for example for use as web colors
Pregenerated Files contain large amounts of downloadable random bits
Pure White Audio Noise for composition or just to test your audio equipment
Jazz Scales to practice improvisation for students of jazz guitar
Samuel Beckett’s randomly generated short prose
DNA Protein Sequence Randomizer (at Bio-Web)

Web Tools and Widgets for Your Pages

Integer Widget Wizard will put a mini-RANDOM.ORG on your web page or blog
Draw Widget Wizard will put the result of a paid drawing on your web page or blog
HTTP API to get true random numbers into your own code
Guidelines describe how to avoid getting in trouble
Banned Hosts lists who didn’t behave and have been blocked

Learn about Randomness

Introduction to Randomness explains what true random numbers are and why they’re interesting
History explains how RANDOM.ORG started and where it is today
Many Testimonials from folks who have found very creative uses for random numbers
Acknowledgements to all the generous folks who have helped out
Quotations about randomness in science, the arts and in life generally
Media Coverage and Scientific Citations lists popular print and scientific mention of the service
News about the latest additions to the site


Real-Time Statistics show how the generator is performing right now
Statistical Analysis explains how you test random numbers for randomness
Bit Tally shows how much randomness has been generated since 1998 (hint: lots!)
Your Quota tells how many random bits you have left for today

Contact and Help

FAQ contains answers to frequently asked questions
Newsletter appears at random intervals, but do sign up
Contact Details in case you want to get in touch

RANDOM.ORG offers true random numbers to anyone on the Internet. The randomness comes from atmospheric noise, which for many purposes is better than the pseudo-random number algorithms typically used in computer programs.

Pick A Number, Any Number

Edited by Oliver Roeder

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Illustration by Guillaume Kurkdjian

Welcome to The Riddler. Every week, I offer up problems related to the things we hold dear around here: math, logic and probability. There are two types: Riddler Express for those of you who want something bite-sized and Riddler Classic for those of you in the slow-puzzle movement. Submit a correct answer for either,Important small print: For you to be eligible, I need to receive your correct answer before 11:59 p.m. EDT on Sunday. Have a great weekend!

“> 1 and you may get a shoutout in next week’s column. If you need a hint, or if you have a favorite puzzle collecting dust in your attic, find me on Twitter.

Riddler Express

From Abijith Krishnan, a simple but intriguing participatory problem:

Submit a positive integer. The person who submits the lowest unique number among all submissions is the winner and is inducted into the exclusive 🏅 Ordinal Order 🏅 of Riddler Nation!

Riddler Classic

From Itay Bavly, a chain-link number problem:

You start with the integers from one to 100, inclusive, and you want to organize them into a chain. The only rules for building this chain are that you can only use each number once and that each number must be adjacent in the chain to one of its factors or multiples. For example, you might build the chain:

4, 12, 24, 6, 60, 30, 10, 100, 25, 5, 1, 97

You have no numbers left to place after 97, leaving you with a finished chain of length 12.

What is the longest chain you can build?

Extra credit: What if you started with more numbers, e.g., one through 1,000?

Solution to last week’s Riddler Express

Congratulations to 👏 Mats Cooper 👏 of Snowmass Village, Colorado, winner of the previous Express puzzle!

In a certain town, 11 fine folks are running in a primary for three at-large seats on the City Commission. Each voter may vote for up to three candidates. This election will reduce the field of candidates from 11 to six. How many different (legal) ways may a voter cast his or her ballot? And how many different outcomes (excluding ties) are there for who advances to November’s general election?

Let’s start by separating out the number of candidates a voter is capable of voting for. They can vote for three, two, one or zero.

If they vote for three candidates, there are “11 choose 3,” or 165, ways to select them. If they vote for two, there are “11 choose 2,” or 55, ways to select them. If they vote for only one, there are 11 ways to choose that candidate. And there’s just one way to vote for zero candidates. Adding all that up gives 232 possible ballots.

As for which candidates advance to November’s general election, there are 11 candidates and six slots, and “11 choose 6” equals 462 outcomes.

Solution to last week’s Riddler Classic

Congratulations to 👏 Josiah Jenkins 👏 of Rugby, North Dakota, winner of the previous Classic puzzle!

There are two warlords: you and your archenemy, with whom you’re competing to conquer castles and collect the most victory points. Each of the 10 castles has its own strategic value for a would-be conqueror. Specifically, the castles are worth 1, 2, 3, … , 9 and 10 victory points. You and your enemy each have 100 soldiers to distribute between any of the 10 castles. Whoever sends more soldiers to a given castle conquers that castle and wins its victory points. (If you each send the same number of troops, you split the points.) Whoever ends up with the most points wins. But now, you have a spy! You know how many soldiers your archenemy will send to each castle. The bad news, though, is that you no longer have 100 soldiers — your army suffered some losses in a previous battle. How many soldiers do you need to have in order to win, no matter the distribution of your opponent’s soldiers?

You need 56 soldiers.

The 10 castles are worth a total of 1 + 2 + … + 9 + 10 = 55 points, meaning you need at least 28 victory points to win. Solver Jack Markley provided an excellent description of the intuition behind the solution:

Since we will have all the knowledge in this battle, we really just need to figure out what the most effective strategy for our enemy would be and then how many soldiers we need to win in that case. War, like everything else involving people who want things, is ruled by economics. My enemy doesn’t want us to get 28 or more points, so they want to make it cost as much as possible — they want to make every castle give an equally poor number of points per soldier required to conquer it. Luckily for my desire to deal with even numbers, 100 is the perfect number of soldiers so that the enemy sets up every castle as requiring two soldiers spent per victory point won with a distribution of 1, 3, 5, 7, 9, 11, 13, 15, 17 and 19 soldiers. With that being the worst distribution for me, I can still win with 56 soldiers by conquering Castles 1 through 7 with a distribution of 2, 4, 6, 8, 10, 12 and 14 — for exactly 28 victory points.

Solvers Daniel Eriksson and Zack Segel approached the problem using a technique called simulated annealing and were kind enough to share their code and graphs. In the image below, you can see how Daniel’s simulations converged to Jack’s mathematical argument about the enemy’s troop distribution above. As the program attempts to find the best distribution to combat your spy, it eventually arrives, after about 8,000 iterations, at the band of bars representing the 1, 3, 5, … soldier distribution described above:

Welcome to The Riddler. ]]>