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 A246975 #14 Feb 24 2020 20:33:37
%S A246975 1,1,3,10,36,121,447,1699,6589,25914,103633,419421,1714463,7068285,
%T A246975 29361629,122764876,516245009,2181957489,9264275600,39495666700,
%U A246975 169000837410,725574719515,3124648750706,13493792787415,58422790497226,253547380435914,1102776319943605
%N A246975 Number of 4-ary plane multitrees with n edges.
%H A246975 Andrew Howroyd, <a href="/A246975/b246975.txt">Table of n, a(n) for n = 0..200</a>
%H A246975 M. Dziemianczuk, <a href="http://dx.doi.org/10.1016/j.disc.2014.07.024">Enumerations of plane trees with multiple edges and Raney lattice paths</a>, Discrete Mathematics 337 (2014): 9-24.
%F A246975 a(n) = Sum_{k=1..n+1} Sum_{i=1..k-1} Sum_{j=0..floor((n-i)/4)} (-1)^j*binomial(k, i)*binomial(i, j)*binomial(n-i, k-i-1)*binomial(n-4*j-1, i-1)/k for n > 0. - _Andrew Howroyd_, Feb 24 2020
%o A246975 (PARI) a(n)={my(m=4); if(n<1, n==0, sum(k=1, n+1, sum(i=1, k-1, sum(j=0, (n-i)\m, (-1)^j*binomial(k, i)*binomial(i, j)*binomial(n-i, k-i-1)*binomial(n-m*j-1, i-1)))/k))} \\ _Andrew Howroyd_, Feb 24 2020
%Y A246975 Cf. A128720 (2-ary case), A246974 (3-ary case).
%K A246975 nonn
%O A246975 0,3
%A A246975 _N. J. A. Sloane_, Sep 14 2014
%E A246975 Terms a(11) and beyond from _Andrew Howroyd_, Feb 24 2020