December 2018 - Challenge

<< November

You get an integer number as a challenge and your goal is to make it a square of an integer number.
To do that, you use two circles with four integers each.
You can change the number you got in steps. In each step we multiply it by the number in the bottom of one of two circles and rotate this circle clock-wise to its next number.

For example, if the two circles are [3,14,15,92] and [6,5,3,5] (the first number is initially at the bottom) then we can solve the input number 42 (i.e. make it a square) by multiplying as follows:

1st circle [3,14,15,92]    42*3=126
2nd circle [6,5,3,5]    126*6=756
2nd circle [5,3,5,6]    756*5=3,780
2nd circle [3,5,6,5]    3780*3=11,340
2nd circle [5,6,5,3]    11340*5=56,700
1st circle [14,15,92,3]    56700*14=793,800
2nd circle [6,5,3,5]    793800*6=4,762,800
1st circle [15,92,3,14]    4762800*15=71,442,000
2nd circle [5,3,5,6]    71442000*5=357,210,000
and getting a square (357,210,000 = 18,900**2).

BTW, There is a much simpler solution, can you find it?

Your challenge, this month, is to find two circles (with four numbers each) such that the same initial state will allow you to solve at least 2,187 different integers between 1 and 65,536.
To make the problem more interesting, you must not use "boring" circles. A circle is called boring if the set of solvable numbers using only this circle is closed under multiplication (i.e. if you can solve X and Y using only this circle, then you can also solve X*Y with it). In the example above, one of the circles (which?) is boring.

Update 3/12: a bonus '*' for two non-boring cycles that create a combined boring solution.

We will post the names of those who submit a correct, original solution! If you don't want your name posted then please include such a statement in your submission!

We invite visitors to our website to submit an elegant solution. Send your submission to the

If you have any problems you think we might enjoy, please send them in. All replies should be sent to:

Challenge: 28/11/2018 @ 12:00 PM EST
Solution: 02/01/2019 @ 12:00 PM EST
List Updated: 10/12/2018 @ 12:00 PM EST

People who answered correctly:

*Alper Halbutogullari (28/11/18 03:46 PM IDT)
Bert Dobbelaere (28/11/18 11:55 PM IDT)
*Arthur Vause (29/11/18 12:53 PM IDT)
*Eden Saig (29/11/18 11:35 PM IDT)
Dominik Reichl (30/11/18 12:35 AM IDT)
*Deane Stewart (30/11/18 05:48 AM IDT)
*Deron Stewart (30/11/18 05:47 PM IDT)
Lorenz Reichel (30/11/18 11:08 PM IDT)
JJ Rabeyrin (01/12/18 12:01 AM IDT)
George Lasry (01/12/18 06:04 AM IDT)
Hugo Pfoertner (02/12/18 03:39 PM IDT)
*Justin Fletcher (03/12/18 02:59 AM IDT)
Harald Bögeholz (03/12/18 09:44 PM IDT)
*Graham Hemsley (04/12/18 03:16 PM IDT)
*David Greer (05/12/18 02:37 AM IDT)
*Thomas Egense (05/12/18 10:26 AM IDT)
*Serino Dario (05/12/18 12:38 PM IDT)
*Fabio Filatrella (05/12/18 05:40 PM IDT)
*Robert Lang (05/12/18 06:22 PM IDT)
*Motty Porat (05/12/18 11:57 PM IDT)
Jingran Lin (06/12/18 11:08 PM IDT)
Almog Yair & NIr Yanowsky (07/12/18 02:19 AM IDT)
*Haye Chan (08/12/18 10:23 AM IDT)
*Dieter Dobbelaere (08/12/18 10:48 PM IDT)
*Armin Krauß (09/12/18 12:18 AM IDT)
*Florian Fischer (09/12/18 02:57 PM IDT)
Peter Gerritson (09/12/18 06:57 PM IDT)