A154119 Numbers n such that binomial(3n,n) is odd and not divisible by 5.

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

Offset

0,3

Comments

From the first 10001 terms of A005809 only 80 are odd and not divisible by 5.

Links

Chai Wah Wu, Table of n, a(n) for n = 0..4000

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

Adjacent sequences: A154116 A154117 A154118 * A154120 A154121 A154122

Keyword

nonn

Author

Zak Seidov, Jan 05 2009

Extensions

Corrected definition - Harvey P. Dale, Jul 19 2011

Status

approved