Did you know that ?

Computer Science Level 3

There exist an amazing Prime Family whose each member when reversed is again a prime number. (eg: 13 and 31 both are prime)

Now, let me know that "What is so special about the $total$ $number$ of such Prime members greater than $5$ and less than $2016$ ?"

Well... It's also a member of that family..! Believe me !

Task: Can you find out what the $number$ is ?

this problem is a part of set Prime Crimes via Computer Science

113 131 313 191 311 181 373

3 solutions

A Former Brilliant Member
Jan 17, 2016

I am assuming that such primes are not one digit. Then, here is my code: (python 3)

def isPrime(n):
    for i in range(2,int(n**0.5)+1):
        if n%i==0:
            return False

    return True

def isprimefamily(n):
    if isPrime(n) and isPrime(int(str(n)[::-1])):
        return True
    else:
        return False

ans=0
for i in range(10,2016):
    if isprimefamily(i):
        ans+=1
    else:
        pass
print (ans)

Vijay Kumar
Jan 23, 2016

Yup. Its true that that number also belongs to that family. [113]

:D Yes.. The problem, when i thought of it before, did not contain that amazing fact. But when I came to the result [113] I was astonished ... then I included the fact in my statement :)

Zeeshan Ali - 5 years, 4 months ago

Zeeshan Ali
Jan 23, 2016

Here is a C++ code to find whether a number is prime or not.

    bool is_prime(int N){
        for (int i=2; i<N/2; i++){
            if (N%i==0){
                return false;
            }
        }
        return true;
    }

I leave the further work on you all, if you don't mind :)

Did you know that ?

this problem is a part of set Prime Crimes via Computer Science

3 solutions

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