A125220 - OEIS

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A125220

Numbers k such that binomial(3k, k) - 1 is prime.

1, 3, 7, 11, 49, 88, 93, 196, 216, 519, 655, 722, 858, 905, 991, 1654, 2277, 3275, 4214, 5047, 5924, 7359, 7953, 11188, 13286, 14626, 14687, 34365, 36014

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OFFSET

1,2

LINKS

Table of n, a(n) for n=1..29.

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

Cf. A125221 (binomial(3k, k) + 1 is prime).