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 A361877 #18 Mar 29 2023 04:57:17 %S A361877 1,2,18,200,2450,31752,426888,5889312,82818450,1181952200,17067389768, %T A361877 248817153312,3656229836168,54086240180000,804670797780000, %U A361877 12030722505475200,180648817621276050,2722858995011344200,41179040356653045000,624643836545795220000,9500832753861545296200 %N A361877 a(n) = binomial(2*n, n) * binomial(2*n - 1, n). %H A361877 Winston de Greef, <a href="/A361877/b361877.txt">Table of n, a(n) for n = 0..829</a> %F A361877 a(n) = (4 - 2 / n)^2 * a(n - 1) for n >= 2. %F A361877 a(n) = A002894(n)/2 for n >= 1. - _Peter Bala_, Mar 28 2023 %p A361877 A361877 := n -> binomial(2*n, n) * binomial(2*n - 1, n): %p A361877 seq(A361877(n), n = 0..20); %p A361877 # Alternative: %p A361877 a := proc(n) option remember; ifelse(n < 2, n + 1, (4 - 2 / n)^2 * a(n - 1)) end: %p A361877 seq(a(n), n = 0..20); %o A361877 (PARI) a(n) = binomial(2*n, n) * binomial(2*n - 1, n); \\ _Michel Marcus_, Mar 28 2023 %Y A361877 Cf. A002894, A000984, A001700. %K A361877 nonn %O A361877 0,2 %A A361877 _Peter Luschny_, Mar 27 2023