A380903 - OEIS

%I #8 Feb 10 2025 09:33:11

%S 2,2,1,2,3,4,10147,24

%N Least positive k such that n^n * k^k - 1 is a prime, or 0 if no such k exists.

%C a(8) > 10^5 or a(8) = 0.

%C a(9) = 0, a(10) = 3, a(11) = 3142, a(12) = 559, a(13) = 3558.

%C a(14) > 10^5 or a(14) = 0.

%F a(n) = A231735(n^n).

%e The least k > 0 such that 4^4*k^k - 1 is a prime is k = 3, so a(4) = 3.

%o (PARI) a(n) = for(k=1, oo, if(ispseudoprime(n^n*k^k-1), return(k))) \\ Does not terminate if a(n) = 0.

%Y Cf. A228175, A231119, A231735.

%K nonn,hard,more,new

%O 0,1

%A _Jason Yuen_, Feb 07 2025