OFFSET
0,1
COMMENTS
a(n) == 3 (mod 4). - Chai Wah Wu, Jan 27 2023
FORMULA
a(n) = A350696(3*2^n).
EXAMPLE
a(1) = 19 because 2^(3*2^1)+19 = 2^6+19 = 83 is the smallest safe prime greater than 64.
PROG
(PARI) a(n) = {my(k=1); pow2 = 2^(3*2^n); while (!(isprime(pow2 + k) && isprime((pow2 + k - 1)/2)), k+=2); k; } \\
(Python)
from sympy import isprime, nextprime
def A360081(n):
m = 1<<3*(1<<n)-1
i = m
while i:=nextprime(i):
if isprime(k:=(i<<1)+1):
return k-(m<<1) # Chai Wah Wu, Jan 27 2023
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Mark Andreas, Jan 25 2023
STATUS
approved