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A191699
Numbers k such that k*(k-1)^k-(k-1)*k^(k-1)-1 is prime.
5
3, 4, 6, 9, 31, 187, 632, 2972
OFFSET
1,1
EXAMPLE
a(1)=3 because 3*2^3-2*3^2-1=5 is prime, a(2)=4 because 4*3^4-3*4^3-1=131 is prime, a(3)=6 because 6*5^6-5*6^5-1=54869 is prime, a(4)=9 because 9*8^9-8*9^8-1=863585783 is prime.
PROG
(Python)
from sympy import isprime
def afind(limit, startk=1):
for k in range(startk, limit+1):
if isprime(k*(k-1)**k - (k-1)*k**(k-1) - 1):
print(k, end=", ")
afind(200) # Michael S. Branicky, Jan 10 2022
CROSSREFS
Cf. A191409 (associated primes).
Sequence in context: A102934 A338061 A350741 * A293272 A192286 A242028
KEYWORD
nonn,hard
AUTHOR
EXTENSIONS
a(8) from Michael S. Branicky, Jan 10 2022
STATUS
approved