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 A023820 #11 Jun 12 2025 08:11:32
%S A023820 0,2,4,4,4,7,7,8,8,8,11,12,9,12,13,12,11,13,14,15,14,17,18,19,16,18,
%T A023820 20,18,18,21,20,21,19,20,22,22,19,22,24,22,21,24,27,29,28,28,29,31,27,
%U A023820 28,29,29,28,34,32,32,31,30,34,34,32,34,36,35,31,32,31,33,33,36,35,36,32,36,40,37,36,38
%N A023820 Sum of exponents in prime-power factorization of C(3n,n-1).
%H A023820 Ivan Neretin, <a href="/A023820/b023820.txt">Table of n, a(n) for n = 1..10000</a>
%F A023820 From _Amiram Eldar_, Jun 12 2025: (Start)
%F A023820 a(n) = A001222(A004319(n)).
%F A023820 a(n) = A023819(n) - A001222(2*n+1) + A001222(n). (End)
%t A023820 Join[{0}, Table[Total[FactorInteger[Binomial[3 n, n - 1]][[All, 2]]], {n, 2, 78}]] (* _Ivan Neretin_, Nov 02 2017 *)
%t A023820 a[n_] := PrimeOmega[Binomial[3*n, n-1]]; Array[a, 100] (* _Amiram Eldar_, Jun 12 2025 *)
%o A023820 (PARI) a(n) = bigomega(binomial(3*n, n-1)); \\ _Amiram Eldar_, Jun 12 2025
%Y A023820 Cf. A001222, A004319, A023819, A023821, A023822, A023823, A023824, A023825.
%K A023820 nonn
%O A023820 1,2
%A A023820 _Clark Kimberling_