OFFSET
1,1
COMMENTS
Primes involved in Cunningham chains of the second kind (2p-1) and not starting or ending them. A059455 is produced by the same rule, but "of the first kind (2p+1)".
LINKS
Chris Caldwell's Prime Glossary, Cunningham chains.
EXAMPLE
a(2)=37 is here because (37 + 1)/2 = 19 and 2*37 - 1 = 73 are both primes;
a(11)=3061 because 1531 -> 3061 -> 6121 through <2p-1> and all are primes;
a(11)=3061, a(18)=6121 and a(31)=12241 are here because they are inside the complete Cunningham chain of the second kind 1531 -> 3061 -> 6121 -> 12241 -> 24481.
MATHEMATICA
Select[Prime[Range[5000]], PrimeQ[(#+1)/2]&&PrimeQ[2#-1]&] (* Vladimir Joseph Stephan Orlovsky, Nov 19 2010 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Alexandre Wajnberg, Aug 31 2005
STATUS
approved