OFFSET
1,1
COMMENTS
Primes p such that {(p-1)/2, p, 2p+1, 4p+3, 8p+7} = {composite, prime, prime, prime, composite}.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
Chris Caldwell's Prime Glossary, Cunningham chains.
Warut Roonguthai, Yves Gallot's Proth.exe and Cunningham Chains.
Eric Weisstein's World of Mathematics, Cunningham Chain.
EXAMPLE
41 is a term because 20 and 325 are composites, and 41, 83, and 167 are primes.
MATHEMATICA
ipccQ[n_]:=Module[{c=(n-1)/2}, PrimeQ[NestList[2#+1&, c, 4]]=={False, True, True, True, False}]; Select[Prime[Range[2000]], ipccQ] (* Harvey P. Dale, Nov 10 2014 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Feb 20 2001
EXTENSIONS
Definition corrected by Alexandre Wajnberg, Aug 31 2005
Offset corrected by Amiram Eldar, Jul 15 2024
STATUS
approved