University Challenge

  Toneman 10:18 30 Nov 2010

Any one watch University Challenge last night. I thought he was wrong to deny UCL the final points, although it wouldn't have given them a win. The question, as I heard it, was "what is the second lowest two digit prime number the digits of which are also prime numbers". The answer given was 13, presumably on the basis that the first was 11. I presume the required answer was 17, but it wasn't made clear that the individual digits had to be different. Am I wrong, have I missed something...

  interzone55 10:31 30 Nov 2010

Both digits of 11 are prime, so the answer is obviously 13...

  mr simon 10:50 30 Nov 2010

1 is not a prime number. The answer is 37.

  interzone55 11:27 30 Nov 2010

At school we were taught that one is a prime number, as it can only be divided by itself and one.

Interestingly Wikipedia claims that one isn't a prime number as it only has one divisor, but you can't always trust Wikipedia...

  natdoor 11:45 30 Nov 2010

Or even 35!

  mr simon 12:10 30 Nov 2010

Or even 37?

  interzone55 12:23 30 Nov 2010

7 x 5 = 35...

  jtt 12:57 30 Nov 2010

It's 57

  natdoor 15:04 30 Nov 2010

Humble apologies. I got carried away and looked for two prime digits and forgot that the result must be prime. Note to myself, read the question!!

  interzone55 15:38 30 Nov 2010

If the "arts graduates at the BBC" were at school at the same time as me, i.e. the 80's, they would have been told by their maths teachers that 1 is a prime number. And under the definition we were given - divisible only by 1 and itself - it is indeed a prime number...

  Forum Editor 16:18 30 Nov 2010

have raged for some time, but on balance it's probably correct to say that mathematicians agree that it isn't, although it used to be considered a prime many years ago.

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