OFFSET
1,3
FORMULA
a(n) = A080778(n+1)/2 for n >= 2. - Amiram Eldar, Dec 06 2018
EXAMPLE
0 is in the sequence since 0!*2^0 + 1 = 2 is prime.
MATHEMATICA
Select[Range[0, 20000], PrimeQ[2^#*#! + 1] &]
PROG
(Magma) [n: n in [0..3*10^2] | IsPrime(Factorial(n)*2^n+1)]; // Vincenzo Librandi, Apr 05 2015
(PARI) for(n=0, 300, if(ispseudoprime(n!*2^n+1), print1(n, ", "))) \\ Derek Orr, Apr 05 2015
(Python)
from sympy import factorial, isprime
for n in range(0, 300):
if isprime(factorial(n)*(2**n)+1):
print(n, end=', ') # Stefano Spezia, Dec 06 2018
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Robert Price, Apr 03 2015
EXTENSIONS
a(6)-a(8), from the data at A080778, added by Amiram Eldar, Dec 06 2018
STATUS
approved