rockdemon said:oooh.... interesting one
Should that read 1 to 9?
Rich.
rockdemon said:oooh.... interesting one
Should that read 1 to 9?
Rich.
richarduk said:Would i be right saying half of the numbers are even and so can be excluded?
Clue - how do you know if a number is divisable by 9
SydneyRoverP6B said:quattro wrote,...Clue - how do you know if a number is divisable by 9
Hello Richard,
Any integer which is divisible by 9 is not prime, except for 9 itself.
Ron.
rockdemon said:1 is irrelevant
2 if a number ends in 0,2,4,6 or 8 it isnt prime. (apart from 2)
3 if a number is n1n2n3n4n5n6n7n8n9 if n1+n2+n3+n4+n5+n6+n7+n8+n9 == multiple of 3 it isnt prime. for 8 it's 36 - for 9 it's 45. So there are no primes in this range???
no need to go on....
Given 3... the answer is zero...????
Rich.
rockdemon said:Hi Richard,
Your hint about looking at single digits did point me the right way...
Was a fun little exercise that one
Rich
darth sidious said:Hold on lads... Are we sure that the reasoning is correct here? I'm not saying you lot are wrong, but something doesn't seem to 'feel' right to me with the reasoning.
Hmm...
quattro said:darth sidious said:Hold on lads... Are we sure that the reasoning is correct here? I'm not saying you lot are wrong, but something doesn't seem to 'feel' right to me with the reasoning.
Hmm...
If a 9 digit number has all of the digits from 1 to 9 in it, then all of the 9 digit numbers have the same digits, just in a different order, and they all add up to 45.
Same with the 8 figure numbers, adding up to 36.
I can't see a problem with it
Richard
You edited your post when I was writing mine Darth