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A154119 Numbers n such that binomial(3n,n) is odd and not divisible by 5. 1
0, 1, 5, 8, 16, 33, 40, 41, 65, 66, 80, 81, 128, 130, 133, 138, 165, 325, 328, 330, 640, 641, 650, 656, 658, 1025, 1026, 1028, 1033, 1040, 1041, 2065, 2066, 2080, 2081, 4128, 4130, 4133, 4138, 4165, 4688, 4690, 4753, 4756, 4776, 4778, 5125, 5128, 5130, 5138 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,3
COMMENTS
From the first 10001 terms of A005809 only 80 are odd and not divisible by 5.
LINKS
FORMULA
A005809(a(n)) is odd and not divisible by 5.
MATHEMATICA
(*M6*)Reap[Do[b=Binomial[3n, n]; If[OddQ[b]&&Mod[b, 10]=/=5, Sow[n]], {n, 100}]][[2, 1]]
bQ[n_]:=Module[{bi=Binomial[3n, n]}, OddQ[bi]&&!Divisible[bi, 5]]; Select[Range[0, 5300], bQ] (* Harvey P. Dale, Jul 19 2011 *)
CROSSREFS
Cf. A125221 Numbers n such that binomial(3n,n)+1 is prime, A005809 Binomial coefficients C(3n,n).
Sequence in context: A340997 A058566 A153363 * A196387 A258787 A185103
KEYWORD
nonn
AUTHOR
Zak Seidov, Jan 05 2009
EXTENSIONS
Corrected definition - Harvey P. Dale, Jul 19 2011
STATUS
approved

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Last modified February 24 05:36 EST 2024. Contains 370291 sequences. (Running on oeis4.)