OFFSET
1,1
COMMENTS
Primes p such that {(p-1)/2, p, 2p+1, 4p+3} = {composite, prime, prime, composite}.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1..1000 from Harvey P. Dale)
Chris Caldwell's Prime Glossary, Cunningham chains.
Warut Roonguthai, Yves Gallot's Proth.exe and Cunningham Chains. [Wayback Machine link]
Eric Weisstein's World of Mathematics, Cunningham Chain.
EXAMPLE
53 is a term because 26 and 215 are composites, and 53 and 107 are primes.
MATHEMATICA
ccftQ[p_]:=Boole[PrimeQ[{(p-1)/2, p, 2 p+1, 4 p+3}]]=={0, 1, 1, 0}; Select[ Prime[ Range[400]], ccftQ] (* Harvey P. Dale, Jun 19 2021 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Feb 20 2001
STATUS
approved