A255598 - OEIS

%I #9 Feb 27 2015 23:28:46

%S 2,2,3,2,3,2,5,2,5,2,3,3,7,2,3,2,3,2,5,2,3,4,5,2,5,3,3,2,5,2,13,3,3,2,

%T 3,2,11,2,5,4,3,3,5,2,3,2,5,3,5,2,9,5,3,4,7,2,3,2,5,2,7,6,3,2,5,2,5,3,

%U 11,4,3,4,13,5,5,2,3,2,7,2,7,4,3,2,5,2,3,2,15,2,7,3,5,2,3,3,11

%N a(n) is the minimal number q>1 such that n(q+1)-1 is prime, or -1 if no such q exists.

%C a(n) <= A060324(n), and a(n) = A060324(n) iff a(n) is prime.

%C Among first 10000 terms, in 2453 cases a(n) < A060324(n). First such cases are for n = 22, 40, 51, 54, 62, 70, 72, 82, 89, 100.

%C Also, among first 10^6 terms, in 324388 cases a(n) < A060324(n).

%o (PARI) a(n) = {my(q = 2); while (! isprime(n*(q+1)-1), q ++); q;} \\ _Michel Marcus_, Feb 27 2015

%Y Cf. A060324.

%K nonn

%O 1,1

%A _Zak Seidov_, Feb 27 2015