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A224471
Numbers n such that 8^n - n is prime.
3
1, 3, 37, 45, 597, 1131, 14203, 112539
OFFSET
1,2
COMMENTS
a(8) > 41000. - Giovanni Resta, Apr 07 2013
a(9) > 2*10^5. - Robert Price, Jan 19 2014
PROG
(Java)
import java.math.BigInteger;
public class A224471 {
public static void main (String[] args) {
BigInteger b8 = BigInteger.valueOf(8);
BigInteger m = BigInteger.valueOf(64);
for(long n=1; ; n+=2) {
BigInteger b = b8.subtract(BigInteger.valueOf(n));
if (b.isProbablePrime(2)) {
if (b.isProbablePrime(80))
System.out.printf("%d\n", n);
}
b8 = b8.multiply(m);
}
}
}
(PARI) forstep(n=1, 10^4, 2, if(ispseudoprime(8^n-n), print1(n, ", "))); /* Joerg Arndt, Apr 07 2013 */
KEYWORD
nonn,hard,more
AUTHOR
Alex Ratushnyak, Apr 06 2013
EXTENSIONS
a(7) from Giovanni Resta, Apr 07 2013
a(8) from Robert Price, Jan 19 2014
STATUS
approved