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A239723
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Least number k such that n^k + (n+1)^k + ... + (n+k-1)^k is prime or 0 if no such number exists.
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1
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2, 1, 1, 2, 1, 0, 1, 0, 2, 0, 1, 2, 1, 2, 0, 6, 1, 0, 1, 0, 6, 2, 1, 2, 2, 0, 0, 0, 1, 2, 1, 2, 0, 2, 2, 0, 1, 0, 2, 0, 1, 2, 1, 0, 0, 0, 1, 6, 0, 2, 0, 0, 1, 0, 0, 0, 0, 6, 1, 2, 1, 0, 0, 0, 2, 0, 1, 0, 2, 2, 1, 2, 1, 0, 0, 6, 0, 0, 1, 0, 0, 2, 1, 2, 2, 0, 2, 0, 1, 2, 6
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OFFSET
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1,1
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COMMENTS
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a(119) = 42. Is a(n) only equal to 0, 1, 2, 6, or 42?
a(n) = 0 is confirmed for k <= 500. See A242927.
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LINKS
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EXAMPLE
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1^1 = 1 is not prime. 1^2+2^2 = 5 is prime. Thus a(1) = 2.
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PROG
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(PARI) a(n)=for(k=1, 500, if(ispseudoprime(sum(i=0, k-1, (n+i)^k)), return(k)))
n=1; while(n<200, print1(a(n), ", "); n+=1)
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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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