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A191699
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Numbers k such that k*(k-1)^k-(k-1)*k^(k-1)-1 is prime.
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5
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OFFSET
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1,1
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LINKS
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EXAMPLE
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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.
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PROG
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(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=", ")
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CROSSREFS
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KEYWORD
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nonn,hard
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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