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A093173
Primes of the form (2^n * n!) - 1.
4
7, 47, 383, 10321919, 51011754393599, 1130138339199322632554990773529330319359999999, 73562883979319395645666688474019139929848516028923903999999999, 4208832729023498248022825567687608993477547383960134557368319999999999
OFFSET
1,1
COMMENTS
Primes resulting from serial multiplication of even numbers, minus 1.
For primes of the form 2^n*n! + 1, trivially a(1)=3, a(2) = 2^259*259! + 1 (593 digits). - Ray Chandler, Mar 27 2004
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..12
FORMULA
Starting with 2, multiply even numbers until the product, minus 1, equals a prime.
a(n) = A117141(n+1). - Alexander Adamchuk, Apr 18 2007
EXAMPLE
a(1) multiplies the first 2 terms, 2*4-1. a(3) multiplies first 4 terms, a(4) multiplies first 8 terms, a(5) multiplies first 13 terms in 12 multiplications.
a(2)=47, formed by 2*4*6 - 1 = 47.
MATHEMATICA
lst={}; Do[If[PrimeQ[p=(2^n*n!)-1], AppendTo[lst, p]], {n, 5!}]; lst (* Vladimir Joseph Stephan Orlovsky, Jan 28 2009 *)
PROG
(PARI) v=[]; for(n=1, 404, if(ispseudoprime(t=n!<<n-1), v=concat(v, t))) \\ Charles R Greathouse IV, Feb 14 2011
CROSSREFS
Cf. A117141 (primes of the form n!! - 1).
Sequence in context: A249477 A108434 A349255 * A368177 A218761 A173772
KEYWORD
nonn
AUTHOR
Enoch Haga, Mar 27 2004
EXTENSIONS
More terms from Ray Chandler, Mar 27 2004
a(8) from Robert Price, Mar 13 2015
STATUS
approved