OFFSET
1,1
COMMENTS
Conjecture: all terms except the first are multiples of 10. - Harvey P. Dale, Mar 26 2015
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
EXAMPLE
1*4 + 1 = 5;
3*4 + 1 = 13;
9*4 + 1 = 37;
27*4 + 1 = 109; 5, 13, 37, 109 are all prime so 4 is in the sequence.
MATHEMATICA
Select[Range[60000], AllTrue[3^Range[0, 3]*#+1, PrimeQ]&] (* The program uses the AllTrue function from Mathematica version 10 *) (* Harvey P. Dale, Mar 26 2015 *)
PROG
(Magma) [n: n in [1..100000] |IsPrime(n+1) and IsPrime(3*n+1) and IsPrime(9*n+1) and IsPrime(27*n+1)] // Vincenzo Librandi, Nov 13 2010
CROSSREFS
KEYWORD
nonn
AUTHOR
Pierre CAMI, Aug 26 2005
STATUS
approved