A030239 - OEIS

A030239

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

%I #24 Apr 19 2019 05:12:46

%S 1,1,1,1,1,18,12,21,102,202,826,708,502,1522,6223,3493,1063,50655,

%T 10051,328426

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

%C The primality test for Proth numbers can be used. - _Thomas Ordowski_, Apr 13 2019

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

%o (PARI) isok(k, n) = isprime(k*2^(2^n) + 1);

%o a(n) = my(k=1); while (!isok(k, n), k++); k; \\ _Michel Marcus_, Apr 15 2019

%Y Cf. A080075, A080076.

%K nonn,more

%O 0,6

%A Alar Leibak (aleibak(AT)cyber.ee)

%E a(11)-a(17) from _Donovan Johnson_, Mar 26 2010

%E a(18)-a(19) from _Donovan Johnson_, Jan 14 2012

%E Name edited by _Thomas Ordowski_, Apr 13 2019