OFFSET
1,1
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..1000
FORMULA
a(n) ~ n log n. - Charles R Greathouse IV, Feb 23 2017
MATHEMATICA
Select[Prime[Range[90]], !PrimeQ[3#(#-1)+1]&] (* Harvey P. Dale, Mar 18 2011 *)
PROG
(PARI) is(n)=isprime(n) && !isprime(3*n*(n-1)+1) \\ Charles R Greathouse IV, Feb 23 2017
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Vincenzo Librandi, Sep 24 2009
EXTENSIONS
2 and 3 removed by R. J. Mathar, Sep 26 2009
STATUS
approved