OFFSET
1,1
COMMENTS
These occur in a proof of nonexistence of a certain type of permutation group for p (Theorem 8 by Ito). - R. J. Mathar, May 29 2011
LINKS
Noboru Ito, Transitive permutation groups of degree p=2q+1, p and q being prime numbers, Bull. AMS 69 (2) (1963), 165-192.
FORMULA
a(n) >> n log^(4) n. - Charles R Greathouse IV, Oct 14 2021
EXAMPLE
(23-1)/2=11, (11-1)/2=5, (5-1)/2=2(prime), ...
MATHEMATICA
lst={}; Do[p=Prime[n]; If[PrimeQ[a=(p-1)/2]&&PrimeQ[b=(a-1)/2]&&PrimeQ[(b-1)/2], AppendTo[lst, p]], {n, 9!}]; lst
PROG
(PARI) is(n)=n%8==7 && isprime(n) && isprime(n\2) && isprime(n\4) && isprime(n\8) \\ Charles R Greathouse IV, Oct 14 2021
(PARI) list(lim)=my(v=List()); forprimestep(p=23, lim\1, 8, if(isprime(p\8) && isprime(p\4) && isprime(p\2), listput(v, p))); Vec(v); \\ Charles R Greathouse IV, Oct 14 2021
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Vladimir Joseph Stephan Orlovsky, Feb 27 2009
STATUS
approved