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 A274056 #7 Jun 09 2016 06:16:42 %S A274056 1,4,90,5040,529200,89812800,22475653200,7791559776000, %T A274056 3576325937184000,2100278686746240000,1536353859354874560000, %U A274056 1369954918280131223040000,1462916144877711556032000000,1843274342545916560600320000000,2706157144150223750531344800000000 %N A274056 Number of unrooted labeled trees on 2n nodes with node degree either one or three. %C A274056 There are no unrooted labeled trees on 2n+1 nodes with node degree either one or three. %H A274056 Math.Stackexchange.com, Marko Riedel et al., <a href="http://math.stackexchange.com/questions/1816933/">Number of labeled trees</a> %p A274056 seq(binomial(2*n, (2*n-2)/2)*(2*n-2)!/2^((2*n-2)/2), n=1..16); %Y A274056 Cf. A000272. %K A274056 nonn %O A274056 1,2 %A A274056 _Marko Riedel_, Jun 08 2016