A240235 Least number k such that k*n^k - 1 is prime. a(n) = 0 if no such number exists.

3, 2, 1, 1, 8, 1, 2, 1, 10, 2, 2, 1, 2, 1, 2, 167, 2, 1, 12, 1, 2, 2, 29028, 1, 2, 3, 10, 2, 26850, 1, 8, 1, 42, 2, 6, 2, 24, 1, 2, 3, 2, 1, 2, 1, 2, 2, 140, 1, 2, 2, 22, 2, 8, 1, 2064, 2, 468, 6, 2, 1, 362, 1, 2, 2, 6, 3, 26, 1, 2, 3, 20, 1, 2, 1, 28, 2, 38, 5, 3024, 1, 2, 81, 858, 1

Offset: 1

Author

Derek Orr, Apr 02 2014

Keywords

• nonn

Comments

a(n) = 1 iff n-1 is prime.

a(145) is either 0 or > 275000. - Robert G. Wilson v, Jan 23 2017

Examples

			1*1^1 - 1 = 0 is not prime. 2*1^2 - 1 = 1 is not prime. 3*1^3 - 1 = 2 is prime. Thus, a(1) = 3.
		

Links

• Robert G. Wilson v, Table of n, a(n) for n = 1..144
• Steven Harvey, Generalized Woodall Primes

Crossrefs

Cf. A066049, A239787, A281141.

Programs

PARI

a(n)=k=1;while(!ispseudoprime(k*n^k-1),k++);return(k); n=1;while(n<100,print(a(n));n+=1)

Extensions

a(23) and a(29) given using link. - Derek Orr, Aug 16 2014