OFFSET
1,1
COMMENTS
Starting with n=3 both a(n) and A023206(n) == 5 mod 6. - Zak Seidov, Oct 23 2009
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..10000
FORMULA
a(n) = 7 + 2*A023206(n). - R. J. Mathar, Oct 05 2009
EXAMPLE
13 is in the sequence because 13 = 7 + 2*3 and 3 are both primes.
MATHEMATICA
Clear[lst, n, f] f[n_]:=PrimeQ[(n-1)/2-3]; lst={}; Do[p=Prime[n]; If[f[p], AppendTo[lst, p]], {n, 7!}]; lst (* Vladimir Joseph Stephan Orlovsky, Oct 13 2009 *)
s={11, 13}; Do[If[PrimeQ[n]&&PrimeQ[(n-7)/2], AppendTo[s, n]], {n, 17, 10^3, 6}]; s (* Zak Seidov, Oct 23 2009 *)
Select[2#+7&/@Prime[Range[200]], PrimeQ] (* Harvey P. Dale, Dec 15 2010 *)
PROG
(PARI) lista(nn) = {forprime(p=2, nn, if (isprime(q=2*p+7), print1(q, ", ")); ); } \\ Michel Marcus, Nov 08 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
Vincenzo Librandi, Oct 04 2009
EXTENSIONS
1089 replaced with 1049 by R. J. Mathar, Oct 05 2009
STATUS
approved