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A093155
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Primes resulting from serial multiplication of even composites, minus 1.
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3
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OFFSET
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1,1
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COMMENTS
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Primes of the form 2^n*(n+1)! - 1.
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LINKS
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FORMULA
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Starting with 4, multiply even composites until the product minus 1 equals a prime.
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EXAMPLE
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a(1) = 3 = 2*2! - 1.
a(2) = 23 = 2^2*3! - 1.
a(3) = 191 = 2^3*4! - 1.
a(4) = 23039 = 2^5*6! - 1.
a(5) = 322559 = 2^6*7! - 1.
a(6) = 5160959 = 2^7*8! - 1.
a(7) = 40874803199 = 2^10*11! - 1.
a(8) = 25505877196799 = 2^12*13! - 1.
a(9) = 2^101*102! - 1 is too large to include.
a(10) = 2^117*118! - 1; a(11) = 2^227*228! - 1. - Jorge Coveiro, Dec 24 2004
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MATHEMATICA
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Select[Table[2^n (n + 1)! - 1, {n, 0, 300}], PrimeQ] (* Vincenzo Librandi, Mar 08 2015 *)
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PROG
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(PARI) for(x=1, 500, if(isprime(2^x*(x+1)!-1), print1(x, ", "))) \\ Jorge Coveiro, Dec 24 2004
(Magma) [a: n in [0..100] | IsPrime(a) where a is 2^n*Factorial(n+1)-1]; // Vincenzo Librandi, Mar 08 2015
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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EXTENSIONS
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The next term is too large to include.
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STATUS
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approved
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