A030239 a(n) is the smallest number k such that k*2^(2^n) + 1 is prime.

1, 1, 1, 1, 1, 18, 12, 21, 102, 202, 826, 708, 502, 1522, 6223, 3493, 1063, 50655, 10051, 328426

Offset: 0

Author

Alar Leibak (aleibak(AT)cyber.ee)

Keywords

• nonn
• more

Comments

The primality test for Proth numbers can be used. - Thomas Ordowski, Apr 13 2019

Crossrefs

Cf. A080075, A080076.

Programs

PARI

isok(k, n) = isprime(k*2^(2^n) + 1);
a(n) = my(k=1); while (!isok(k, n), k++); k; \\ Michel Marcus, Apr 15 2019

Formula

a(n) = min{a : a > 0 and (a*2^2^n)! == -1 (mod a*2^2^n+1)}.

Extensions

a(11)-a(17) from Donovan Johnson, Mar 26 2010

a(18)-a(19) from Donovan Johnson, Jan 14 2012

Name edited by Thomas Ordowski, Apr 13 2019