OFFSET
1,1
COMMENTS
Odd prime factors of numbers of the form 3^3^i + 1: for odd primes p, p divides 3^3^i + 1 if and only if the multiplicative order of 3 modulo p is 2 times a power of 3 not exceeding 3^i.
EXAMPLE
37 is a term since the multiplicative order of 3 modulo 37 is 18 = 2*3^2, which means that 37 is a factor of 3^3^2 + 1.
163 is a term since the multiplicative order of 3 modulo 163 is 162 = 2*3^4, which means that 163 is a factor of 3^3^4 + 1.
PROG
(PARI) isA367649(n) = my(d); isprime(n) && (n!=3) && ((d=znorder(Mod(3, n)))%2==0) && isprimepower(3*d/2)
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Jianing Song, Nov 25 2023
EXTENSIONS
a(28)-a(31) from Chai Wah Wu, Nov 26 2023
STATUS
approved