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A334993
Numbers k such that 2*3^k + 1 is prime and divides Phi(3^m, 2).
0
1, 5, 9, 17, 57, 65, 897, 4217, 6225, 152529, 3648969, 5570081
OFFSET
1,2
COMMENTS
A subset of odd values from A003306.
If p = 2*3^k + 1 is prime then p divides 2^(3^k) + (-1)^k, due to Euler's criterion.
Only odd terms of sequence A003306 can divide the cyclotomic expression Phi(3^m, 2); none of the even terms of sequence A003306 can divide 2^3^k-1 and therefore cannot divide Phi(3^m, 2).
PROG
(PARI) dp(n)=Mod(2, 2*3^n+1)^3^n==1;
forstep(n=1, 6225, 2, if(dp(n), print1(n, ", ")))
CROSSREFS
Cf. A003306.
Sequence in context: A336139 A295627 A300128 * A262484 A228956 A233584
KEYWORD
nonn,hard,more
AUTHOR
Serge Batalov, May 18 2020
STATUS
approved