OFFSET
1,1
COMMENTS
The definition indicates that each chain is exactly 5 primes long (i.e. the chain cannot be a subchain of a longer one). That's why this sequence is different from A057328 which gives also primes included in longer chains (thus not "starting" them), as 16651, starting a seven primes chain, or 33301, second prime of the same seven primes chain.
LINKS
Chris Caldwell's Prime Glossary, Cunningham chains.
G. Löh, Long chains of nearly doubled primes, Math. Comp. vol. 53 no. 188 (1989) pp 751-759.
EXAMPLE
6841 is here because: 6841 through <2p-1> -> 13681-> 27361-> 54721-> 109441 and the chain ends here since 2*109441-1=13*113*149 is composite.
MAPLE
isA110022 := proc(p) local pitr, itr ; if isprime(p) then if isprime( (p+1)/2 ) then RETURN(false) ; else pitr := p ; for itr from 1 to 4 do pitr := 2*pitr-1 ; if not isprime(pitr) then RETURN(false) ; fi ; od: pitr := 2*pitr-1 ; if isprime(pitr) then RETURN(false) ; else RETURN(true) ; fi ; fi ; else RETURN(false) ; fi ; end: for i from 2 to 200000 do p := ithprime(i) ; if isA110022(p) then printf("%d, ", p) ; fi ; od: # R. J. Mathar, Jul 23 2008
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Alexandre Wajnberg, Sep 03 2005
EXTENSIONS
Edited and extended by R. J. Mathar, Jul 23 2008
STATUS
approved