OFFSET
1,1
COMMENTS
The decimal expansion of 1/a(n) will produce a stream of a(n)-1 pseudo-random digits. - Reinhard Zumkeller, Feb 10 2009
The condition in the name is sufficient for primes p such that the decimal expansion of 1/p recurs after p-1 digits, which is the maximum-possible cycle length. - Robert A. J. Matthews, Oct 31 2023
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..1000
Robert A. J. Matthews, Maximally periodic reciprocals, Bull. Institute of Mathematics and Its Applications, vol. 28, p. 147-148, 1992.
Wikipedia, Sophie Germain prime
FORMULA
a(n) = 2*A000355(n)+1. - Reinhard Zumkeller, Feb 10 2009
MAPLE
q:= p-> irem(p, 40) in {7, 19, 23} and andmap(isprime, [p, (p-1)/2]):
select(q, [$1..10000])[]; # Alois P. Heinz, Oct 31 2023
MATHEMATICA
Select[Prime[Range[1000]], MatchQ[Mod[#, 40], 7|19|23] && PrimeQ[(#-1)/2]&] (* Jean-François Alcover, Feb 07 2016 *)
PROG
(PARI) is(n)=my(k=n%40); (k==7||k==19||k==23) && isprime(n\2) && isprime(n) \\ Charles R Greathouse IV, Nov 20 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
More terms from Reinhard Zumkeller, Feb 10 2009
STATUS
approved