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A219789
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Least prime in the form x*y-1 with x > 0, y > 0 and x + y = n > 3.
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1
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2, 3, 7, 5, 11, 7, 23, 17, 19, 11, 23, 13, 47, 29, 31, 17, 83, 19, 71, 41, 43, 23, 47, 71, 131, 53, 103, 29, 59, 31, 167, 149, 67, 101, 71, 37, 383, 113, 79, 41, 83, 43, 167, 89, 251, 47, 263, 97, 191, 101, 103, 53, 107, 109, 311, 113, 223, 59, 431, 61, 239, 353
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OFFSET
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4,1
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COMMENTS
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LINKS
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EXAMPLE
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a(6)=7 since 6=2+4 with 2*4-1=7 prime.
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MATHEMATICA
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Do[Do[If[PrimeQ[k(n-k)-1]==True, Print[n, " ", k(n-k)-1]; Goto[aa]], {k, 1, n/2}]; Print[n, " ", counterexample]; Label[aa]; Continue, {n, 4, 100}]
Table[k = 1; While[p = k*(n - k) - 1; k <= n/2 && ! PrimeQ[p], k++]; If[k > n/2, Print["counterexample at n=", n]; p = 0]; p, {n, 4, 100}] (* T. D. Noe, Nov 28 2012 *)
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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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