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A109908
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a(n) = greatest prime of the form k*(n-k)-1, or 0 if no such prime exists.
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2
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0, 0, 0, 3, 5, 7, 11, 11, 19, 23, 29, 31, 41, 47, 53, 59, 71, 79, 89, 83, 109, 71, 131, 139, 149, 167, 181, 191, 197, 223, 239, 251, 271, 263, 293, 307, 311, 359, 379, 383, 419, 439, 461, 479, 503, 503, 521, 571, 599, 599, 647, 659, 701, 727, 743, 719, 811, 839
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OFFSET
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1,4
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COMMENTS
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Conjecture: a(n) > 0 for n > 3.
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LINKS
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PROG
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(PARI) { a(n)=forstep(k=n\2, 1, -1, if(isprime(k*(n-k)-1), return(k*(n-k)-1))); return(0) } \\ Max Alekseyev, Oct 04 2005
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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