OFFSET
1,1
COMMENTS
Primes p such that 10*p+9, 100*p+99, 1000*p+999 and 10000*p+9999 are also primes. - Vincenzo Librandi, Aug 04 2010
LINKS
John Cerkan, Table of n, a(n) for n = 1..10000
FORMULA
a(n) == 9 or 13 (mod 14). - John Cerkan, Oct 09 2016
MATHEMATICA
Select[Prime[Range[20000]], AllTrue[Rest[NestList[10#+9&, #, 4]], PrimeQ]&] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Feb 16 2020 *)
PROG
(Magma) [n: n in [1..5000000] | IsPrime(n) and IsPrime(10*n+9) and IsPrime(100*n+99) and IsPrime(1000*n+999) and IsPrime(10000*n+9999)]; // Vincenzo Librandi, Aug 04 2010
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
Definition clarified by Harvey P. Dale, Feb 16 2020
STATUS
approved