OFFSET
1,1
COMMENTS
2*prime(n)+1 is prime iff a(n) = 2*prime(n)+1.
EXAMPLE
For n=2, prime(2)=3 and a(2)=7 since 2^(2*3)-1 = 63 = 3^2*7.
For n=4, prime(4)=7 and a(4)=43 since 2^(2*7)-1 = 16383 = 3*43*127.
For n=5, prime(5)=11 and a(5)=23 since 2^(2*11)-1 = 4194303 = 3*23*89*683.
PROG
(PARI) forprime(p=2, 163, Ap=factor(2^(2*p)-1)[2, 1]; print1(Ap, ", "))
(Python)
from sympy import prime, primefactors
def A363673(n):
m = (1<<(prime(n)<<1))-1
a, b = divmod(m, 3)
while not b:
m = a
a, b = divmod(m, 3)
return min(primefactors(m)) # Chai Wah Wu, Jun 26 2023
CROSSREFS
KEYWORD
nonn
AUTHOR
Alain Rocchelli, Jun 14 2023
STATUS
approved