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A243404
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Least number k such that n^k - n^(k-1) - ... - n^2 - n - 1 is prime.
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0
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1, 1, 2, 1, 2, 1, 2, 2, 2, 1, 564, 1, 10, 2, 2, 1, 14, 1, 2, 2, 8, 1, 2, 5, 2, 3, 2, 1, 2, 1, 252, 3, 20, 2, 6, 1, 2, 2, 4, 1, 24, 1, 2, 2, 2, 1, 2, 3, 2, 17, 24, 1, 2, 2, 2, 3, 4, 1, 2, 1, 4, 11, 2, 2, 2, 1, 2, 555, 2, 1, 8, 1, 12, 3, 2, 3, 6, 1, 4, 6, 680, 1, 6, 2, 2, 3, 132
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OFFSET
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3,3
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COMMENTS
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a(n) = 1 iff n-1 is prime.
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LINKS
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EXAMPLE
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5^1 - 5^0 = 4 is not prime. 5^2 - 5^1 - 5^0 = 19 is prime. Thus a(5) = 2.
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PROG
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(PARI) a(n)=for(k=1, 10^3, if(ispseudoprime(n^k-sum(i=0, k-1, n^i)), return(k)))
n=1; while(n<100, print1(a(n), ", "); n++)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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