A224471 Numbers k such that 8^k - k is prime.

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

Links

Table of n, a(n) for n=1..8.

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 */

Crossrefs

Cf. A048744, A058037, A057908, A058046, A058829, A224470, A224469, A224469.

Sequence in context: A037000 A042333 A106103 * A286637 A106996 A338751

Adjacent sequences: A224468 A224469 A224470 * A224472 A224473 A224474

Keyword

nonn,hard,more,changed

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