OFFSET
1,2
COMMENTS
After 1, a(n) is congruent to 4 or 9 (mod 10), this means that a(n) is of the form 5k-1. Clearly, each term is not divisible by 3 and 11.
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..1000
FORMULA
a(n) = (A007530(n)-3)/2. [Michael B. Porter, Mar 21 2013]
MATHEMATICA
Select[Range[50000], Union[PrimeQ[2 # + {3, 5, 9, 11}]]=={True}&]
PROG
(Magma) [n: n in [1..50000] | forall{2*n+k: k in [3, 5, 9, 11] | IsPrime(2*n+k)}];
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Vincenzo Librandi, Mar 13 2013
STATUS
approved