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 A001340 M1858 N0736 #44 Jun 30 2017 08:49:38
%S A001340 2,8,38,212,1370,10112,84158,780908,8000882,89763320,1094915222,
%T A001340 14431179908,204423631178,3097603939952,50001759773870,
%U A001340 856665220770332,15526612798028258,296825612428239848,5969385443426556422,125983618731675924020,2784204907403441680442
%N A001340 E.g.f.: 2*exp(x)/(1-x)^3.
%C A001340 a(n) = A001339 (n+1) - A001339 (n)..3-1=2, 11-3=8, 49-11=38... [_Gary Detlefs_, Jun 06 2010]
%D A001340 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
%D A001340 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H A001340 T. D. Noe, <a href="/A001340/b001340.txt">Table of n, a(n) for n = 0..100</a>
%H A001340 E. Biondi, L. Divieti, G. Guardabassi, <a href="http://dx.doi.org/10.4153/CJM-1970-003-9">Counting paths, circuits, chains and cycles in graphs: A unified approach</a>, Canad. J. Math. 22 1970 22-35.
%H A001340 Philip Feinsilver and John McSorley, <a href="http://dx.doi.org/10.1155/2011/539030">Zeons, Permanents, the Johnson Scheme, and Generalized Derangements</a>, International Journal of Combinatorics, Volume 2011, Article ID 539030, 29 pages; doi:10.1155/2011/539030.
%F A001340 a(n) = 2 * A082030(n).
%F A001340 a(n) = floor((n+1)*(n+1)!*e) - floor(n*n!*e) [_Gary Detlefs_, Jun 06 2010]
%F A001340 a(n) = {exp(1)*(n^2+n+1)*n!} for n>0, where {x} is the neareast integer, proposed by _Simon Plouffe_, March 1993.
%F A001340 G.f.: (1-x)/x/Q(0) -1/x, where Q(k)= 1 - x - x*(k+2)/(1 - x*(k+1)/Q(k+1)); (continued fraction). - _Sergei N. Gladkovskii_, Apr 22 2013
%F A001340 G.f.: W(0)/x - 1/x, where W(k) = 1 - x*(k+2)/( x*(k+3) - 1/(1 - x*(k+1)/( x*(k+1) - 1/W(k+1) ))); (continued fraction). - _Sergei N. Gladkovskii_, Aug 26 2013
%F A001340 Conjecture: a(n) +(-n-3)*a(n-1) +(n-1)*a(n-2)=0. - _R. J. Mathar_, May 03 2017
%t A001340 nn = 20; Range[0, nn]! CoefficientList[Series[2*Exp[x]/(1 - x)^3, {x, 0, nn}], x] (* _T. D. Noe_, Jun 28 2012 *)
%K A001340 nonn,easy
%O A001340 0,1
%A A001340 _N. J. A. Sloane_ and _Simon Plouffe_
%E A001340 Error in description corrected Jan 30 2008
%E A001340 More terms from _N. J. A. Sloane_, Jan 30 2008