My Competitions (Index)

This page lists my current competitions and also what type of puzzles each competition mainly focuses on. No competitions are “dumbed down” as someone has claimed. They are simply of different types. Enjoy 🙂


#1. Arithmetical

#2. Logical

#3. Lateral thinking (thinking outside the square)

#4. Lateral thinking

#5. Magic squares

#6. Counters and coins

#7. Feedback on my blog

#8. Sudoku

Here are the rules again:


  1. Email your answers one at a time (anytime after the questions have a link above) to me using my Contact page.
  2. You must start with question 1 and answer each question in order. i.e. 1,2,3,4,5,6.
  3. You cannot try the next question until Alan confirms you have got your current question right (starting with question 1).
  4. You must include the question with your answer (copy and paste the question).
  5. Alan’s answers are final (unless you can prove him wrong).
  6. There is not a prize (only bragging rights and maybe a certificate). Daud and Fiona have generously provided a picture of a chocolate fish with a bite out of the end if you would like one :).
  7. No cheating from the Internet (except for competition #8).
  8. Don’t post any answers here or anywhere else.

Enjoy 🙂



Competition #8: Sudoku (Internet searches)

Today’s competition is all about searching the Internet. You do not need to know how to solve Sudoku for this competition.

Sudoku uses a 9×9 grid with 81 cells. Starting with a grid with some cells already filled in with numbers, you have to complete the grid according to the rules using only the numbers 1 to 9. All Sudoku puzzles must have a unique solution.

The numbers initially filled in are called givens.  If there are originally 25 numbers, say, filled in before you start, you have 25 givens (numbers that you have already been given).

Many Sudoku puzzles have been found (i.e. uniquely solvable) that have 17 givens. No one knew if there was any Sudoku the existed with 16 givens. Computer searches were undertaken to find out if any Sudoku had 16 givens.

No Sudoku have been found with only 16 givens. A “proof” that none exist has been published.

Use the Internet to answer the questions below according to the rest of my rules.


Q1. Approximately how many Sudoku have been found with 17 givens?

Q2. Find a more precise number of known Sudoku with 17 givens. You may have to look for a list of Sudoku with 17 givens.

Q3. Find a “Sudoku” with 16 givens that has only two solutions.

Q4. Who published the proof (give authors’ names) that there are no Sudoku with 16 givens? What date was this article published?

Q5. Many computer programs exist to solve a Sudoku. Find the code for a computer “program” (procedure) that is about five lines long or less. How long is the shortest known program?

Q6. If you have a Sudoku with 17 givens, how can you find out if a Sudoku exists with 16 givens within it? i.e. A Sudoku with 16 givens that has the 17th number (given) in its solution (same cell).

Good luck 🙂