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
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