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A117141
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Primes of the form n!! - 1.
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51
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OFFSET
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1,1
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REFERENCES
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G. Balzarotti and P. P. Lava, Le sequenze di numeri interi, Hoepli, 2008, p. 158.
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LINKS
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FORMULA
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EXAMPLE
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6!! - 1 = 6*4*2 - 1 = 48 - 1 = 47, which is prime.
8!! - 1 = 8*6*4*2 - 1 = 384 - 1 = 383, which is prime.
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MAPLE
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SFACT:= proc(n) local i, j, k; for k from 1 by 1 to n do i:=k; j:=k-2; while j >0 do i:=i*j; j:=j-2; od: if isprime(i-1) then print(i-1); fi; od: end: SFACT(100);
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MATHEMATICA
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PROG
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(PARI) print1(2); for(n=1, 1e3, if(ispseudoprime(t=n!<<n-1), print1(", "t))) \\ Charles R Greathouse IV, Jun 16 2011
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CROSSREFS
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Cf. A093173 = primes of the form (2^n * n!) - 1.
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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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