OFFSET
1,1
COMMENTS
The first 5 known Fermat primes from A019434 are terms.
Conjecture: also primes p such that 2*phi(p-2) = p-1 (i.e., primes in A232720).
a(7) > 10^25. - Max Alekseyev, Feb 02 2024
PROG
(Magma) [n: n in [3..10000000] | IsPrime(n) and (n-1) mod EulerPhi(n-2) eq 0]
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Jaroslav Krizek, Feb 25 2015
STATUS
approved