A191717 Numbers k such that k*(k-1)^k - (k-1)*k^(k-1) + 1 is prime.

3, 5, 18, 23, 78, 131, 177

Offset: 1

Author

Juri-Stepan Gerasimov, Jun 12 2011

Keywords

• nonn
• hard
• more

Examples

			a(1)=3 because 3*2^3-2*3^2+1=7 is prime, a(2)=5 because 5*4^5-4*5^4+1=2621 is prime.
		

References

• a(8) > 20000. - Michael S. Branicky, Apr 11 2025

Crossrefs

Cf. A191699, A191715.

Programs

PARI

is(n)=ispseudoprime(n*(n-1)^n-(n-1)*n^(n-1)+1) \\ Charles R Greathouse IV, Jun 13 2017