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 A013499 #30 Jul 26 2017 07:52:55
%S A013499 1,1,8,54,512,6250,93312,1647086,33554432,774840978,20000000000,
%T A013499 570623341222,17832200896512,605750213184506,22224013651116032,
%U A013499 875787780761718750,36893488147419103232,1654480523772673528354
%N A013499 a(n) = 2*n^n, n >= 2, otherwise a(n) = 1.
%C A013499 For n>=1, a(n) gives the number of alternating plane trees (trees such that the son of each vertex is ordered) on the set of vertices {1,2,..,n+1} (Chauve et al.). See A007889 for the non-ordered case. - _Peter Bala_, Aug 30 2011
%H A013499 Vincenzo Librandi, <a href="/A013499/b013499.txt">Table of n, a(n) for n = 0..300</a>
%H A013499 C. Chauve, S. Dulucq and A. Rechnitzer, <a href="https://doi.org/10.1006/jcta.2000.3121">Enumerating alternating trees</a>, J. Combin. Theory Ser. A 94 (2001), 142-151.
%H A013499 Frank Schmidt and Rodica Simion, <a href="https://doi.org/10.1007/BF01834201">Card shuffling and a transformation on S_n</a>, Aequationes Math. 44 (1992), no. 1, 11-34.
%F A013499 For n>1, resultant of x^n+1 and n(x-1). - _Ralf Stephan_, Nov 20 2004
%t A013499 lst={};Do[a=n^n;b=(n+1)^(n+1);ab=b-a;ba=b+a;AppendTo[lst,ba-ab],{n,4!}];lst (* _Vladimir Joseph Stephan Orlovsky_, Mar 20 2009 *)
%o A013499 (PARI) a(n) = if (n<=1, 1, 2*n^n); \\ _Michel Marcus_, Jul 26 2017
%Y A013499 Cf. A007889.
%K A013499 nonn
%O A013499 0,3
%A A013499 _N. J. A. Sloane_
%E A013499 Name edited by _Michel Marcus_, Jul 26 2017