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 A000449 M4700 N2009 #60 Jul 06 2023 05:36:21
%S A000449 1,0,10,40,315,2464,22260,222480,2447445,29369120,381798846,
%T A000449 5345183480,80177752655,1282844041920,21808348713320,392550276838944,
%U A000449 7458455259940905,149169105198816960,3132551209175157490,68916126601853463240
%N A000449 Rencontres numbers: number of permutations of [n] with exactly 3 fixed points.
%D A000449 J. Riordan, An Introduction to Combinatorial Analysis, Wiley, 1958, p. 65.
%D A000449 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
%D A000449 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H A000449 T. D. Noe, <a href="/A000449/b000449.txt">Table of n, a(n) for n = 3..100</a>
%H A000449 FindStat - Combinatorial Statistic Finder, <a href="http://www.findstat.org/St000022">The number of fixed points of a permutation</a>
%H A000449 <a href="/index/Per#IntegerPermutationCatAuto">Index entries for sequences related to permutations with fixed points</a>
%F A000449 a(n) = Sum_{j=2..n-3} (-1)^j*n!/(3!*j!) = A008290(n,3).
%F A000449 For n >= 3 a(n) = C(n, 3) * A000166(n-3) = 1/6 * n! * Sum_{k=0..n-3} (-1)^k/k!. - Dan Fux (dan.fux(AT)OpenGaia.com or danfux(AT)OpenGaia.com), Apr 14 2001
%F A000449 E.g.f.: 1/(exp(x)*(1-x))*(x^3)/6. - _Wenjin Woan_, Nov 20 2008
%F A000449 E.g.f.: x^3*exp(-x)/(3!*(1-x)). - _Geoffrey Critzer_, Nov 03 2012
%F A000449 a(n) ~ n! * exp(-1)/6. - _Vaclav Kotesovec_, Mar 17 2014
%F A000449 a(n) = n*a(n-1) - (-1^n)*n*(n-1)*(n-2)/6, a(n) = 0 for n= 0, 1, 2. - _Chai Wah Wu_, Sep 23 2014
%F A000449 O.g.f.: (1/6)*Sum_{k>=3} k!*x^k/(1 + x)^(k+1). - _Ilya Gutkovskiy_, Apr 13 2017
%F A000449 D-finite with recurrence (-n+3)*a(n) +n*(n-4)*a(n-1) +n*(n-1)*a(n-2)=0. - _R. J. Mathar_, Jul 06 2023
%p A000449 # with k fixed-points:
%p A000449 G:=exp(-z)*z^k/((1-z)*k!: Gser:=series(G,z,21):
%p A000449 for n from k to 20 do a(n)=n!*coeff(Gser,z,n): end do: # _Paul Weisenhorn_, May 30 2010
%t A000449 Table[Subfactorial[n - 3]*Binomial[n, 3], {n, 3, 22}] (* _Zerinvary Lajos_, Jul 10 2009 *)
%o A000449 (PARI) my(x='x+O('x^66)); Vec( serlaplace(exp(-x)/(1-x)*(x^3/3!)) ) \\ _Joerg Arndt_, Feb 19 2014
%o A000449 (Python)
%o A000449 A000449_list, m, x = [], 1, 0
%o A000449 for n in range(3,21):
%o A000449 x, m = x*n + m*(n*(n-1)*(n-2)//6), -m
%o A000449 A000449_list.append(x) # _Chai Wah Wu_, Sep 23 2014
%Y A000449 Cf. A008290.
%Y A000449 A diagonal of A008291.
%Y A000449 Cf. A170942.
%K A000449 nonn,easy
%O A000449 3,3
%A A000449 _N. J. A. Sloane_