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 A125220 Numbers k such that binomial(3k, k) - 1 is prime. 7
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS 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). Cf. A066699 (binomial(2k, k) + 1 is prime). Cf. A066726 (binomial(2k, k) - 1 is prime). Sequence in context: A358311 A217383 A005372 * A016081 A287301 A105762 Adjacent sequences: A125217 A125218 A125219 * A125221 A125222 A125223 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

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Last modified March 27 18:55 EDT 2023. Contains 361575 sequences. (Running on oeis4.)