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 A089643 #31 Apr 24 2021 08:51:46
%S A089643 0,1,1,1,2,1,1,2,2,1,2,2,2,3,1,1,2,2,1,2,2,2,3,2,2,3,3,1,2,2,2,3,2,2,
%T A089643 3,3,2,3,3,3,4,1,1,2,2,1,2,2,2,3,2,2,3,3,1,2,2,2,3,2,2,3,3,2,3,3,3,4,
%U A089643 2,2,3,3,2,3,3,3,4,3,3,4,4,1,2,2,2,3,2,2,3,3,2,3,3,3,4,2,2,3,3,2,3,3,3,4,3
%N A089643 3^a(n) divides C(3n,n); 3-adic valuation of A005809.
%H A089643 Antti Karttunen, <a href="/A089643/b089643.txt">Table of n, a(n) for n = 0..19683</a>
%F A089643 a(n) = A007949(A005809(n)). - _Antti Karttunen_, Jul 29 2017
%F A089643 a(n) = A054861(3*n) - A054861(2*n) - A054861(n). - _David A. Corneth_, Jul 29 2017
%F A089643 a(n) = A053735(2*n)/2. - _Amiram Eldar_, Feb 21 2021
%t A089643 Table[IntegerExponent[Binomial[3 n, n], 3], {n, 0, 104}] (* _Michael De Vlieger_, Jul 29 2017 *)
%o A089643 (PARI) a(n)=valuation(binomial(3*n,n),3)
%o A089643 (Python)
%o A089643 from sympy import binomial
%o A089643 def a007949(n): return 0 if n%3 else a007949(n//3) + 1
%o A089643 def a(n): return a007949(binomial(3*n, n))
%o A089643 print([a(n) for n in range(151)]) # _Indranil Ghosh_, Jul 29 2017
%Y A089643 Cf. A005809, A007949, A053735, A054861.
%K A089643 nonn,easy
%O A089643 0,5
%A A089643 _Benoit Cloitre_, Jan 01 2004