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A126782
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Primes of the form [n! mod (n!!+1)]/2, with n>=1.
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0
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OFFSET
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1,1
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COMMENTS
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LINKS
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EXAMPLE
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n=6 n!=720 n!!=48 [n! mod (n!!+1)]/2 = (720 mod 49)/2 = 34/2 = 17
n=7 n!=5040 n!!=105 [n! mod (n!!+1)]/2 = (5040 mod 106)/2 = 58/2 = 29
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MAPLE
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P:=proc(n) local i, j, k, w; for i from 2 by 1 to n do k:=i; w:=i-2; while w>0 do k:=k*w; w:=w-2; od; j:=(i! mod (k+1))/2; if isprime(j) then print(j); fi; od; end: P(1000);
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MATHEMATICA
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Select[Table[Mod[n!, n!!+1]/2, {n, 200}], PrimeQ] (* Harvey P. Dale, Apr 15 2018 *)
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CROSSREFS
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KEYWORD
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hard,nonn
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AUTHOR
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STATUS
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approved
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