This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A154119 #16 Aug 11 2025 18:11:42
%S A154119 0,1,5,8,16,33,40,41,65,66,80,81,128,130,133,138,165,325,328,330,640,
%T A154119 641,650,656,658,1025,1026,1028,1033,1040,1041,2065,2066,2080,2081,
%U A154119 4128,4130,4133,4138,4165,4688,4690,4753,4756,4776,4778,5125,5128,5130,5138
%N A154119 Numbers k such that binomial(3k,k) is odd and not divisible by 5.
%C A154119 From the first 10001 terms of A005809 only 80 are odd and not divisible by 5.
%H A154119 Chai Wah Wu, <a href="/A154119/b154119.txt">Table of n, a(n) for n = 0..10000</a>
%F A154119 A005809(a(n)) is odd and not divisible by 5.
%t A154119 (*M6*)Reap[Do[b=Binomial[3n,n];If[OddQ[b]&&Mod[b,10]=/=5,Sow[n]],{n,100}]][[2,1]]
%t A154119 bQ[n_]:=Module[{bi=Binomial[3n,n]},OddQ[bi]&&!Divisible[bi,5]]; Select[Range[0,5300],bQ] (* _Harvey P. Dale_, Jul 19 2011 *)
%Y A154119 Cf. A125221 Numbers n such that binomial(3n,n)+1 is prime, A005809 Binomial coefficients C(3n,n).
%K A154119 nonn
%O A154119 0,3
%A A154119 _Zak Seidov_, Jan 05 2009
%E A154119 Corrected definition - _Harvey P. Dale_, Jul 19 2011