OFFSET
1,1
EXAMPLE
If n=279 then (7*n + 1)/2 = 977 (prime).
MATHEMATICA
Select[Range[500], PrimeQ[(7#+1)/2]&] (* Harvey P. Dale, May 07 2011 *)
PROG
(PARI) is(n)=isprime((7*n+1)/2) \\ Charles R Greathouse IV, Jun 13 2017
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Parthasarathy Nambi, Nov 16 2005
STATUS
approved