What is the 100th prime whose each digit is also a prime except 0 ?
Consider 1 as a prime.
Such first few primes are: 1, 2, 3, 5, 7, 11, 13, 17, 23 ……
where 1st prime is 1 and 9th prime is 23.
Note that 19 is ignored, because 9 is not a prime
Source : http://www.youngprogrammer.com/
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// Author : Gultu // Dept : CTE, UIU #include <stdio.h> bool is_prime (int x) { for ( int i = 2; i * i <= x; i++ ) { if ( x % i == 0 ) return false; } return true; } bool prime_digit (int x) { while ( x ) { switch (x % 10) { case 4 : case 6 : case 8 : case 9 : return false; } x /= 10; } return true; } int main () { int count = 9; int variable = 31; while ( count < 100 ) { if ( is_prime (variable) && prime_digit (variable) ) count++; variable += 2; } printf ("%d\n", variable - 2); return 0; }