Sudoku

What are the Sudoku rules?  ↥

The Sudoku rules are quite simple, each number from 1 to 9 may only appear once in each row, column and quadrant. The Sudoku playing field consists of 9 columns and 9 rows, which are then divided into 9 3 x 3 quadrants.

What determines the difficulty of a Sudoku?  ↥

The level of difficulty is determined solely by the techniques required to solve it.

Many people believe that the number of numbers given determines the difficulty. This is wrong! There are many puzzles where only 20 numbers are given, but these can be solved by beginners using simple techniques, while there are others where you have to combine different solving techniques for the last 20 numbers to get ahead, so even experienced puzzlers can really work up a sweat.

So the techniques required alone determine whether a Sudoku is difficult or easy. The need for a clear solution alone determines the minimum number of numbers that must be given. For example, at least 17 numbers must be given, but more may be necessary to enable a clear solution.

Many of the easy Sudoku puzzles you see printed somewhere are only half solved.

Sudoku history  ↥

Who invented Sudoku?  ↥

The American Howard Garns is considered the inventor, who published a puzzle called Number Place in 1979. The name Sudoku was only given to the number puzzle later in Japan. However, the first squares with numbers already existed in China around 2800 BC, and squares with numbers continued to appear throughout history, forming the basis for today’s number puzzle.

Magic squares  ↥

The first records of squares with numbers come from China and date back to around 2800 BC; these were so-called magic squares. Magic squares are available in different edge lengths, all numbers are entered in such a way that the sums of the individual columns and rows are identical, there were usually no specifications for the numbers.

In the 8th century, the first puzzles based on magic squares were created in what is now Iraq, where they were called Buduh. In Europe, the first records date back to the 16th century. One of the most famous magic squares can be found in the copperplate engraving Melancholia (Melencolia I) by Albrecht Dürer.

Euler’s square  ↥

In the 18th century, the Swiss mathematician Leonhard Euler worked on magic squares, but used a predetermined number of characters corresponding to the edge length of the square and the additional rule that each character may only occur once in each column and row.

Euler first used Latin letters instead of numbers, which is why it is also called a Latin square. An Eulerian square with an edge length of 9, i.e. 9x9 squares, is already quite similar to today’s Sudoku, but it still lacked the division into 9 additional 3x3 blocks.

Number Place  ↥

In 1979, the first Sudoku appeared in the American puzzle magazine “Dell Pencil Puzzles & Word Games” under the name Number Place, the author was kept secret.

Only later did the puzzle inventor Will Shorts find out that the architect Howard Garns had invented the puzzle Number Place, making Howard Garns the inventor of Sudoku. Colleagues of Garns also reported that he had worked on a kind of crossword puzzle with numbers, but kept it secret.

Sudoku in Japan  ↥

In 1984, the Japanese puzzle publisher Nikoli began printing these number puzzles, Nikoli also gave it its name, first calling it “Suuji wa dokushin ni kagiru”, which translates roughly as “Numbers must stand individually”, then shortening it to Sudoku and registering it as a trademark in Japan. This is why it is still known as “Number Place” in Japan.

In 1986, Nokoli added the rule that clues must be in symmetrical patterns, and only then did this number puzzle become very popular in Japan, where it is still the most popular logic puzzle today.

Sudoku in Europe  ↥

It was only after the New Zealander Wayne Gould got to know Sudoku in Japan and developed the computer program “Pappocom Sudoku”, which generated new Sudoku at the touch of a button and which he then sold to various newspapers in the USA and Europe from 2004 onwards that it also became very popular in Europe and worldwide.

Wayne Gould has earned many millions from the sale of his program and books and was on Time Magazine’s list of the 100 most influential people in the world in 2006.

The fact that Sudoku is not protected by copyright, meaning that anyone can create and sell Sudoku puzzles, naturally also contributed to its rapid worldwide spread.

Sudoku Topical  ↥

The website Sudoku-Topical.com was published in 2007. The basic idea was to offer Sudokus every day in a format optimized for printing. Other websites already offered some for printing, but here you needed a sheet of paper for each puzzle and then another sheet for the solution. Right from the start, Sudoku Aktuell offered PDF files with 12 Sudoku puzzles including solutions on 4 A4 pages.

Later, Sudoku-Topical.com was expanded to include an online Sudoku, which was also designed to be very easy to use. There are now over 50,000 PDF files in the PDF archive on Sudoku-Topical.com, i.e. 600,000 Sudoku puzzles, all of which can be solved online. And 120 new ones are added every day

In the latest revision of Sudoku-Topical.com, the number of Sudoku per page can be selected for the PDF downloads, 1 to 12 Sudoku per DIN A4 page, so there is a suitable size for everyone. The online Sudoku has also been completely redesigned and is now state of the art with various new functions.

Why is Sudoku so popular?  ↥

The principle of Sudoku is not protected, so anyone can create and publish them. Gradually, many magazines started to print them. And since Sudoku is a logic puzzle with numbers, it offers the same puzzle fun across countries/languages/cultures. In Japan, however, the name “Sudoku” is registered as a trademark, so the original name “Number Place” is still common there.

What does Sudoku mean?  ↥

Sudoku is the abbreviation for “Suuji wa dokushin ni kagiru”, which is Japanese and loosely translated means “Numbers must stand individually”. The name comes from the Japanese puzzle publisher Nikoli when they started publishing Sudoku puzzles in Japan.

What makes a real Sudoku?  ↥

In a real Sudoku there is only one unique solution, this can only be found through logic and only as many numbers are given as are necessary to make this unique solution possible. On Sudoku-Aktuell.de there are only real Sudoku!

Sudoku Variants  ↥

What Sudoku variants are there?  ↥

In addition to the normal Sudoku, there are now also many variants, starting with those with fewer or more columns/rows, with symbols instead of numbers, with additional rules, such as the X Sudoku, in which the numbers 1-9 may only occur once in the diagonals, Sudoku in which basically several overlap, up to Sudoku in which you first have to calculate the starting numbers yourself.

X-Sudoku  ↥

In this variant, the numbers 1-9 may only appear once on each of the two diagonals between the opposite corners that form an X.

Multi Sudoku  ↥

This consists of several Sudokus in which individual blocks overlap. An example is the Samurai Sudoku, consisting of 5 Sudokus forming an x, one in the middle and each of the 4 blocks in the corners are also a corner block of another. There are also variants with 8, 13 or more normal Sudokus

Comparison Sudoku  ↥

In the comparison Sudoku, the side lines of the individual fields have < and > signs (larger/smaller) and thus show the ratio of the numbers to the numbers in the respective neighboring fields. A comparison sudoku does not require any predefined numbers.

Even-Odd-Sudoku  ↥

It is indicated for individual fields whether the number to be entered is even or odd.

Jigsaw Sudoku  ↥

Also called Nonomino Sudoku, here the 3x3 blocks are not present, instead there are 9 areas each consisting of 9 contiguous fields, in these areas each number may only occur once.

Circle Sudoku  ↥

The playing field is a circle, divided into 6 rings and 6 segments (like a pizza), resulting in 36 fields, here the numbers 1-6 are entered, so that each number occurs only once in each ring and each segment.

Killer Sudoku  ↥

Here some of the fields are grouped arbitrarily and the sum of the numbers within the respective grouping is given, so in addition to logic, mental arithmetic is also trained.

Sudoku in education  ↥

Primary school teacher Bernd Wehren has developed various arithmetic and spelling exercises based on Sudoku and has published books on the subject. Here, for example, the starting numbers must first be determined through arithmetic problems.

Is there a Sudoku championship?  ↥

There is both a world championship and different national championships. The World Sudoku Championship (WSC) has been held once a year since 2006 by the World Puzzle Federation. There are individual and team competitions at the World Championship.

Sudoku FAQ  ↥

For which age groups is Sudoku suitable?  ↥

Children as young as primary school age can solve Sudoku. There are also variations where the starting numbers have to be calculated first and can therefore be used as practice material in elementary school. From primary school age upwards, these logic puzzles are suitable for all age groups and have fans in all age groups.

What do I train with Sudoku?  ↥

As Sudoku is a logic puzzle, it trains both logical thinking and the ability to concentrate.

Is Sudoku good for the brain?  ↥

Yes, Sudoku engages the brain, sharpens the ability to think logically and concentrate and keeps the brain fit, especially in old age.

Why is Sudoku so popular?  ↥

Sudoku is based purely on logic, has simple rules, can be learned quickly, a Sudoku is solved in a short time and the first successes come quickly. So it offers puzzle fun completely independent of language/country/culture.

New partner site  ↥

As the online sudoku was getting a bit long in the tooth, we decided to give it a complete overhaul. As the changes were more extensive than planned, we decided to test it on a new website first, and then in several languages. So you can now see and test the revised version of the online Sudoku webapp on Sudoku120.com: Sudoku Online.

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Sudoku Puzzles

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Sudoku