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Blazing goIITian

Joined:	31 May 2007
Post:	520

6 Apr 2009 18:15:32 IST

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Find the first two primes above 1 million, which digit sums are also prime. The solution is the con

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Find the first two primes above 1 million, which digit sums are also prime.The solution is the concatination of the two numbers,Example: If the first number is 1,234,567and the second is 2,345,678,your solution is 12345672345678

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Bipin Dubey

Forum Expert

Joined: 23 Jan 2007

Posts: 7942

7 Apr 2009 16:05:45 IST

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I am using the fact that prime numbers can only be of the form 6k+1 or 6k+5.

Program :

n=1000000;

count1=0;

while(count1<2)

{

count2=0;

if(n%6==1 || n%6==5)

{

for(i=2;i<=sqrt(n);i++)

{

if(n%i==0)

count2=count2+1;

}

if(count2==0)

{

count1=count1+1;

printf("%d",n);

}

n=n+1;

}

else

n=n+1;

}

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