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 A273974 #20 Sep 03 2024 08:25:36
%S A273974 0,0,1,3,6,13,32,82,226,651,1939,5946,18637,59736,194898,645742,
%T A273974 2167325,7359262,25237989,87325031,304549332,1069685013,3781189896,
%U A273974 13443608964,48049822995,172568075048,622514907195,2254799747130,8197867118026,29909486953987,109477635390870
%N A273974 Number of primes <= n-th Catalan number.
%H A273974 Amiram Eldar, <a href="/A273974/b273974.txt">Table of n, a(n) for n = 0..39</a> (calculated using Kim Walisch's primecount)
%H A273974 Kim Walisch, <a href="https://github.com/kimwalisch/primecount">Fast C++ prime counting function implementation (primecount)</a>.
%F A273974 a(n) = A000720(A000108(n)). - _Michel Marcus_, Nov 10 2016
%t A273974 Table[PrimePi[CatalanNumber[n]], {n, 0, 27}]
%o A273974 (Magma) [#PrimesUpTo(Catalan(n)): n in [0..18]];
%Y A273974 Cf. A000108, A000720, A054782, A277062, A277063.
%K A273974 nonn
%O A273974 0,4
%A A273974 _Vincenzo Librandi_, Nov 10 2016
%E A273974 a(28)-a(30) from _Amiram Eldar_, Sep 03 2024