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 A073774 #13 Mar 02 2024 10:37:31 %S A073774 0,0,0,4,68,376,1440,4736,14272,40576,110592,291840,750592,1890304, %T A073774 4677632,11403264,27443200,65306624,153878528,359399424,832831488, %U A073774 1916272640,4380950528,9957277696,22510829568,50642026496,113413980160 %N A073774 Number of plane binary trees of size n+3 and height n. %H A073774 Henry Bottomley and Antti Karttunen, <a href="/A073345/a073345.txt">Derivations of the formulas for the diagonals of A073345 & A073346</a>. %F A073774 a(n) = A073345(n+3, n). %F A073774 a(n < 3) = 0, a(3) = 4, a(n) = 1/12 * 2^(n-1) * (2*n^3 + 9*n^2 - 23*n - 78) or a(n) = 2^(n-2) * |A073775(n-3)| from n >= 3 onward. %p A073774 A073774 := n -> `if`((n < 3),0,(2^(n-2))*abs(A073775(n-3))); %Y A073774 Cf. A014480, A073345, A073773, A073775. %K A073774 nonn %O A073774 0,4 %A A073774 _Antti Karttunen_, Aug 11 2002