A327661 Least number k > n - 2 such that k*n^k - 1 is prime.

3, 2, 2, 3, 8, 19, 18, 7, 10, 11, 252, 43, 563528, 98, 14, 167, 18, 28, 410, 44, 200, 140, 29028, 124, 68, 79, 2420, 47, 26850, 63, 2454, 140, 42, 164, 38, 62, 740, 67, 448, 51, 84, 135, 404882, 43, 84, 140, 140, 115, 710, 2390, 46640, 261, 60, 72, 2064, 414

Offset: 1

Author

Jeppe Stig Nielsen, Sep 21 2019

Keywords

• nonn
• hard

Comments

Different version of A240235. Some authors, like Caldwell (link), require that k + 2 > n before they use the term generalized Woodall for a prime of form k*n^k - 1.

Examples

			To find a(11), consider numbers k*11^k - 1 where k > 9. The first time it is prime, is for k = 252, so a(11) = 252.
		

Links

• Jeppe Stig Nielsen, Table of n, a(n) for n = 1..144
• Chris K. Caldwell, The Top Twenty: Generalized Woodall.

Crossrefs

Cf. A240235, A327660, A240234.

Programs

PARI

for(b=1,+oo,for(k=b-1,+oo,if(ispseudoprime(k*b^k-1),print1(k,", ");next(2))))