- Has all prime digits
- Forms primes with its first two digits.
- Forms primes with its last two digits.
Puzzle for 25 Jun 2009
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Go4Expert Founder
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| 25Jun2009,09:43 | #1 |
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Find a three digit prime number which
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Invasive contributor
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| 25Jun2009,10:35 | #2 |
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I say 373
Has all prime digits - All are Prime 3, 7 Forms primes with its first two digits - Forms Prime with first 2 digits 37 Forms primes with its and last two digits. - Forms Prime with Last two - 73 The last condition looks incomplete. There was no condition of uniqueness of digits There was no condition like least 3 digit prime 
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Pro contributor
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| 25Jun2009,10:50 | #3 |
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179 - 3 unique digit prime no.
17 is a prime no. 79 is prime no. |
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Invasive contributor
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| 25Jun2009,10:52 | #4 |
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Quote:
Originally Posted by Mridula  Sorry Mridula for Yesterday |
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Go4Expert Founder
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| 25Jun2009,11:01 | #5 |
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Quote:
Originally Posted by nimesh Quote:
Originally Posted by nimesh I would like to also see a reason as to how you landed to the number you have as answer. |
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Invasive contributor
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| 25Jun2009,11:27 | #6 |
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"The last condition looks incomplete."
I mean the sentence formation is incorrect. Which you have corrected now...haha What reason would you like? [btw, you didn't asked earlier to specify the reason] I just looked at the list of prime numbers and checked with the conditions you gave. Other numbers that I thought were: 113, 131, 137, 173, 197, 311, 313, 317 - But 1 is not a prime number So the first number that I got was 373 |
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Mentor
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| 25Jun2009,12:44 | #7 |
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All possible results are
237 373 537 737 Code:
int is_prime(int n)
{
if (n==2) return 1;
if (n<3) return 0;
if (!(n%2)) return 0;
for (int i=3; i*i<=n; i+=2)
{
if (!(n%i))
return 0;
}
return 1;
}
int _tmain(int argc, _TCHAR* argv[])
{
for (int i=100; i<1000; i++)
{
int digits[3];
int temp=i;
digits[2]=temp%10; temp/=10;
digits[1]=temp%10; temp/=10;
digits[0]=temp%10;
temp=i;
int ms100,ls100;
ms100=digits[0]*10+digits[1];
ls100=digits[1]*10+digits[2];
if (is_prime(digits[0]) && is_prime(digits[1]) && is_prime(digits[2]))
{
if (is_prime(ms100) && is_prime(ls100))
{
printf("%d\n",i);
}
}
}
return 0;
}
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~ Б0ЯИ Τ0 С0δЭ ~
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| 25Jun2009,13:08 | #8 |
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LOL @ xpi0t0s, you brute-forced the solution for such a simple question !!
I mean, shabbir didn't even mention the word "smallest". So, that was really easy to figure out a 3-digit number. Congrats nimesh. @ shabbir: So, you changed the posting time today (by almost -12 hours) !!  I'll have to wait till 2morrow. Last edited by SaswatPadhi; 25Jun2009 at 13:11.. |
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Invasive contributor
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| 25Jun2009,14:07 | #9 |
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xpi0t0s - 237 is not a prime number (237 = 3 * 79) List of Prime Numbers
Thanks Saswat, but the winner is not yet confirmed by Shabbir
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Mentor
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| 25Jun2009,14:27 | #10 |
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Whoops, you're right, neither are 537 and 737 so the only result is 373. Adding
Code:
if (is_prime(i)) |