guardian sudoku-ness

i noticed today that the guardian now has its very own sudoku puzzle. since this is puzzle number 24 from saturday, i can surmise that they've had this for less than a month and i've simply not noticed.

the one thing that impresses me is, however, the starting grid for the puzzle. it consists of two squares rotated 45 degrees right in which the numbers 1-9 are placed in order, top to bottom then left to right. one square is at top right, one at bottom left. preserving rotational symmetry (180 degrees about the diagonal) while removing reflectional, two numbers are also placed in the top-left and bottom right squares.

which brings me to another question - is the starting setup of a sudoku puzzle copyright? i guess it probably is, and apologies to the guardioan for the following (although it is fair use, as a quote for review purposes or a citation for educational purposes perhaps?) i also assume that the finishing grid might be copyrighted/able, since it is concievable someone could solve your puzzle then produce another starting position that is derived from your finhing grid... or should i just be pleased with the guardian's hard work on the design of (at the very least) puzzle number twenty four, medium:

...|...|1.. 1
.5.|..2|.4. 5 2 4
6..|.3.|5.7 6 3 5 7
---+---+--- 6 8
...|..6|.8. 1 9
..1|...|9.. 2 4
.2.|4..|... 3 5 7 6
---+---+--- 6 8 2
3.5|.7.|..6 9

now, i've been trundling around the web and found some interesting sudoku related things... firstly, this is an automated web sudoku solver which also gives a list of the steps it took to find the solution. there's a blog which gives the solutions to various newspaper puzzles as well. regarding my query about the total number of sudoku grids possible, this blog thread seems to have come up with an answer - the maths is as hard as i thought it would be, and i'm sure it would have taken me a lot longet to work it out - i was still nowhere near. the number is apparently 6,670,903,752,021,072,936,960 which is equivalent to 9! x 72^2 x 2^7 x 27,704,267,971. see also the wikipedia entry for sudoku for a lot of interesting information...


phone scam hoaxes

i recieved the following email at work today:

Phone Fraud - Warning
We have been advised of a telephone fraud currently in operation - this applies to home and work telephones, landlines and mobiles.

If you receive one of these fraudulent calls, upon answering the telephone you will hear a recorded message congratulating you on winning an all expenses trip to an exotic location. You will then be asked to press 9 to hear further details. If you press 9 you will be connected to a premium rate line that costs approximately ?20 per minute. Even if you disconnect immediately, it will remain connected for a minimum of 5 minutes costing around ?100. The final part of the call involves you being asked to key in your postcode and house number, which has other serious consequences. After a further 2 minutes you will receive a message informing you that you are not one of the lucky winners. The total bill by then will be ?100 (though Trading Standards have confirmed to me that there's some question about the actual costs, but they're still extortionate) .

Since the calls are originating from outside the UK, BT and other telephone companies are left relatively powerless to act. The only safe solution is to HANG UP before the message prompts you to dial 9, even safer HANG UP on any unsolicited 'free offer calls'.

There is another scam operating on mobile phones as well. A missed call comes up. The number is 0709 020 3840, the last four numbers may vary, but certainly the first four will remain the same. If you call this number back you will be charged ?50 per minute. People have complained about their phone bills, once they have realised the cost of the call, but apparently this is completely legal. So beware, do not call back numbers beginning with '0709'.

needless to say, it's all a hoax or urban myth. basically, there are no phone lines that cost more that GBP 1.50 per minute. any that do cost this much will start '09' - these numbers are regulated by ICSTIS. anyway, when called by someone, pressing digits on your phone will never cause any amount to be added to your bill - this is just impossible. as long as someone else calls you, they will be paying for the call. the number '9' has no special functions when pressed during a call.

any phone number beginning with '0709' is a 'find me anywhere' personal number, as defined by OFCOM, and they have been allocated to various companies. admittedly, the pricing structure for these numbers can be somewhat confusing, ranging from local rate to mobile-equivalent rate, and including fixed price per call. however the BT pricelist lists the rate bands. these will be charged by BT at no more than 50p per minute.

a summary of the charges, in pence per minute is shown below:

0709 01 k 37.5p
0709 02 pn2 50.0p
0709 03 pn3 49.0p
0709 04 pn4 26.0p
0709 05 pn6 20.0p
0709 06 j 32.0p
0709 07 pn2 50.0p
0709 08 k 37.5p
0709 09 k 37.5p
07091 k 37.5p
0709 20 k 37.5p
0709 21 k 37.5p
0709 22 k 37.5p
0709 23 k 37.5p
0709 24 k 37.5p
0709 25 k 37.5p
0709 26 k 37.5p
0709 27 k 37.5p
0709 28 k 37.5p
0709 29 k 37.5p
0709 40 pn2 50.0p
0709 41 pn4 26.0p
0709 42 k 37.5p
0709 43 k 37.5p
0709 44 pn9 23.5p
0709 45 j 32.0p
0709 46 pn2 50.0p
0709 47 k 37.5p
0709 48 e 5.0p
0709 49 k 37.5p
0709 65 pn2 50.0p
0709 66 pn2 50.0p
0709 67 pn2 50.0p
0709 68 pn7 4.0p (plus 50.0p fixed cost)
0709 69 pn5 17.0p
07099 0 d 16.7p
07099 2 f 30.0p
07099 4 pn2 50.0p
07099 5 k 37.5p
07099 6 k 37.5p
07099 8 pn2 50.0p