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 A087298 #11 Sep 01 2024 09:36:58
%S A087298 1,4,7,10,11,16,18,22,23,26,31,34,35,39,41,46,47,50,53,56,57,64,66,70,
%T A087298 71,74,78,81,82,86,88,94,95,98,101,104,105,110,112,116,117,120,127,
%U A087298 130,131,135,137,142,143,146,149,152,153,159,161,165,166
%N A087298 Exponent of 2 in the prime factorization of (3n)!.
%H A087298 Amiram Eldar, <a href="/A087298/b087298.txt">Table of n, a(n) for n = 1..10000</a>
%F A087298 a(2n) = a(n) + 3n.
%F A087298 a(n) = Sum_{k>=1} floor(3n/2^k).
%F A087298 a(n) = A011371(3*n) = 3*n - A036555(n). - _Amiram Eldar_, Sep 01 2024
%e A087298 (3*5)! = 2^11 * 638512875, so a(5) = 11.
%t A087298 a[n_] := 3*n - DigitCount[3*n, 2, 1]; Array[a, 100] (* _Amiram Eldar_, Sep 01 2024 *)
%o A087298 (PARI) a(n)=valuation((3*n)!,2)
%Y A087298 Cf. A011371 (n!), A005187 ((2n)!), A036555.
%K A087298 nonn,easy
%O A087298 1,2
%A A087298 _Ralf Stephan_, Oct 20 2003