please empty your brain below
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No more than two prime numbers each, thanks.
diamond geezer | Homepage | 08.03.18 - 7:02 a.m. | #
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Since I'm in first, I'll go for the easy ones: 3 and 7
martin | 08.03.18 - 7:03 a.m. | #
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My favourite number - 73, and its reverse, 37
Waterhouse | 08.03.18 - 7:08 a.m. | #
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157 and 743
Tim | 08.03.18 - 7:11 a.m. | #
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751
Madison | 08.03.18 - 7:13 a.m. | #
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11 and 17
Whiff | 08.03.18 - 7:15 a.m. | #
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5 & 13
Ken | 08.03.18 - 7:22 a.m. | #
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79 and 97
Anonymous | 08.03.18 - 7:23 a.m. | #
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43 & 71
Roger French | Homepage | 08.03.18 - 7:24 a.m. | #
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179 and 953
Gordon | 08.03.18 - 7:29 a.m. | #
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19 & 139
dg writes: No, neither of those.
Still Anon | 08.03.18 - 7:31 a.m. | #
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1.
*hides*
Wolf | 08.03.18 - 7:38 a.m. | #
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31 and 37
Kevin | 08.03.18 - 7:41 a.m. | #
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53
59
Patrickov | 08.03.18 - 7:44 a.m. | #
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347 & 937.
Mike Scott | 08.03.18 - 7:56 a.m. | #
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@Wolf, as I understand it, 1 is not generally accepted as a prime number, see https://en.wikipedia.org/wiki/Prime_number#Primality_of_one.
Regards
zin92 | 08.03.18 - 7:59 a.m. | #
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Since when was 19 not prime?
Hardcastle | 08.03.18 - 8:00 a.m. | #
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If we just go in straight lines, and as the order matters, there are more distinct one, two and three digit numbers in that block than I expected: I make it 9 singles, 40 pairs, and 16 triples (although some repeats). So nearly half of them are prime.
Andrew | 08.03.18 - 8:02 a.m. | #
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19 is prime, but it's not in the grid. Nowhere will you find a 1 next to a 9.
Mike Scott | 08.03.18 - 8:02 a.m. | #
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739 + 457
MS | 08.03.18 - 8:02 a.m. | #
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So far: 3, 5, 7, 11, 13, 17, 31, 37, 43, 53, 59, 71, 73, 79, 97, 157, 179, 347, 457, 739, 743, 751, 937, 953.
Six left.
(there'll be another post once this is solved, and then another post before midday)
diamond geezer | Homepage | 08.03.18 - 8:04 a.m. | #
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113 and 311
the orange one | 08.03.18 - 8:18 a.m. | #
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311 and 113.
This packs in a lot of fun into a small space and I've never seen anything quite like it before. Very good!
Chris | Homepage | 08.03.18 - 8:20 a.m. | #
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359 and 971
zin92 | 08.03.18 - 8:22 a.m. | #
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Bah, beaten to it by the orange one because I was busy being polite.
Open question: are there any other sets of nine digits that will hide more than 30 prime numbers? I suppose there are only 1 000 000 000 possible squares to try to check, which sounds like it could be done reasonably practicably on a home PC.
dg writes: That's my next question...
Chris | Homepage | 08.03.18 - 8:25 a.m. | #
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47
Lorenzo | 08.03.18 - 8:31 a.m. | #
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9^9 = 387,420,489 rather than 1,000,000,000 squares to check?
Isn't this still too large a number to check on a PC though?
Regards
zin92 | 08.03.18 - 8:36 a.m. | #
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And 41
Lorenzo | 08.03.18 - 8:38 a.m. | #
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And that's the lot! Full set of answers...
3, 5, 7, 11, 13, 17, 31, 37, 41, 43, 47, 53, 59, 71, 73, 79, 97, 113, 157, 179, 311, 347, 359, 457, 739, 743, 751, 937, 953, 971
diamond geezer | Homepage | 08.03.18 - 8:39 a.m. | #
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Are we allowed to say that it raises the question rather than begs the question? Or is such pedantry not welcomed :-)?
R.O. Beethoven | 08.03.18 - 10:32 a.m. | #
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I haven't managed to check all the possible grids - but assumed it was most likely that the corners would be odd numbers other than 5. In this restricted case, 30 is indeed the most number of primes (unless I've made a mistake of course).
Miff | 08.03.18 - 11:11 a.m. | #
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Thanks Miff!
diamond geezer | Homepage | 08.03.18 - 11:47 a.m. | #
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@zin92 0 is also a digit, though admittedly not one that appears in any prime numbers! That's presumably where 10^9 came from.
Muzer | 08.03.18 - 12:43 p.m. | #
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I’m with you on the pedantry front R. O. Beethoven
Keith | 08.03.18 - 2:03 p.m. | #
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@muzer
0 appears in many prime numbers - the first is 101.
timbo again | Homepage | 08.03.18 - 3:16 p.m. | #
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@timbo again D'oh, complete brainfart there! Of course it does!
Muzer | 08.03.18 - 3:57 p.m. | #
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