OFFSET
1,2
MATHEMATICA
Do[f=Binomial[3n, n]-1; If[PrimeQ[f], Print[n]], {n, 1, 1000}]
Select[Range[4300], PrimeQ[Binomial[3#, #]-1]&] (* Harvey P. Dale, Aug 24 2017 *)
PROG
(PARI) is(n)=binomial(3*n, n)-1 \\ Charles R Greathouse IV, Feb 17 2017
CROSSREFS
KEYWORD
hard,more,nonn
AUTHOR
Alexander Adamchuk, Nov 25 2006
EXTENSIONS
a(16)-a(19) from Robert G. Wilson v, Nov 26 2006
a(20)-a(29) from Robert Price, Apr 23 2019
STATUS
approved