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

1,1

Comments

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

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

Links

Robert G. Wilson v, Table of n, a(n) for n = 1..144

Steven Harvey, Generalized Woodall Primes

Example

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.

Prog

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

Crossrefs

Cf. A066049, A239787, A281141.

Sequence in context: A291117 A293181 A229345 * A092742 A316564 A214742

Adjacent sequences: A240232 A240233 A240234 * A240236 A240237 A240238

Keyword

nonn

Author

Derek Orr, Apr 02 2014

Extensions

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

Status

approved