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 A301270 #18 Apr 15 2018 18:48:19
%S A301270 4,20,144,1372,16384,236196,4000000,77948684,1719926784,42417997492,
%T A301270 1157018619904,34599023437500,1125899906842624,39618312131623748,
%U A301270 1499253470328324096,60724508119499193196,2621440000000000000000,120167769980326767578964,5829995856912430117421056,298461883710362842247633948,16079954871362414694843285504
%N A301270 Number of labeled trees on n vertices containing two fixed non-adjacent edges.
%H A301270 M. Lavrov and M. Riedel, math.stackexchange.com, <a href="https://math.stackexchange.com/questions/2691262/">Number of labelled trees on n vertices containing two fixed non-adjacent edges</a>
%F A301270 a(n) = 0 for n < 4, 4 * n^(n-4) = 4 * A008785(n-4) otherwise.
%e A301270 The edges {1,2} and {3,4} can form a tree by being joined by an edge in four ways (two possibilities for each edge).
%t A301270 Array[4 #^(# - 4) &, 21, 4] (* _Michael De Vlieger_, Mar 19 2018 *)
%Y A301270 Cf. A000169, A000272, A008785.
%K A301270 nonn
%O A301270 4,1
%A A301270 _Marko Riedel_, Mar 17 2018