OFFSET
1,1
EXAMPLE
a(1) = 3 is prime and 2*3 + 1 = 7 also but not 4*3 + 3 = 15.
MATHEMATICA
Select[Prime[Range[410]], And[PrimeQ[2 # + 1], CompositeQ[4 # + 3]] &] (* Michael De Vlieger, Apr 19 2024 *)
PROG
(Python)
import sympy as sp
l = []
for i in range(2, 2800):
if sp.isprime(i) and sp.isprime(2*i + 1) and not(sp.isprime(4*i + 3)):
l.append(i)
print(l)
CROSSREFS
KEYWORD
nonn
AUTHOR
Alexandre Herrera, Apr 15 2024
STATUS
approved