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Search: id:A130827
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| A130827 |
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Least k >= 1 such that k^n+n is semiprime, or 0 if no such k exists. |
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+0
2
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| 3, 2, 1, 3, 1, 7, 3, 1, 1, 11, 2, 7, 1, 1, 7, 3, 5, 23, 4, 1, 1, 3, 2, 1, 1, 21, 14, 11, 12, 7, 16, 1, 1, 1, 26, 37, 1, 1, 4, 21, 6, 31, 4, 25, 1, 71, 14, 1, 10, 1, 10, 371, 36, 1, 3, 1, 1, 185, 2, 43, 1, 49, 104, 1, 18, 205, 70, 1, 2, 33, 38, 541, 1, 105, 8, 1, 24, 395, 30, 3, 1, 71, 20, 1, 1, 1
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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k^n+n can be prime for not all n's (cf. A072883). What about semiprime k^n+n? For which n's a(n)=0? Cf. A097792 (n such that x^n+n is reducible), A072883 (Least k >= 1 such that k^n+n is prime, or 0 if no such k exists).
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LINKS
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Sean A. Irvine, Table of n, a(n) for n=1,...,100.
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EXAMPLE
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a(1)=3, a(2)=2 and a(3)=1 because
3^1+1=2^2+2=1^3+3=4=2*2 (semiprime),
a(4)=3 because 3^4+4=35=5*7 (semiprime), a(5)=1
because 1^5+1=6=2*3 (semiprime), a(6)=7 because
7^6+6=117655=5*23531 (semiprime).
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CROSSREFS
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Cf. A072883, A097792.
Adjacent sequences: A130824 A130825 A130826 this_sequence A130828 A130829 A130830
Sequence in context: A112745 A036585 A164848 this_sequence A070309 A130784 A119910
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KEYWORD
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nonn,new
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AUTHOR
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Zak Seidov (zakseidov(AT)yahoo.com), Aug 18 2007
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EXTENSIONS
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More terms from Sean A. Irvine (sairvin(AT)xtra.co.nz), Oct 20 2009
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