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 A105928 #32 Jun 01 2018 01:56:12 %S A105928 0,0,0,6,72,780,8520,97650,1189104,15441048,213816240,3152287710, %T A105928 49369524600,819340272036,14373198453432,265869427695690, %U A105928 5173710021214560,105683257864542000,2261482144869433824,50598160483438733238,1181568482279829616680,28750554997809594831420 %N A105928 a(n) = ((n^3 - 4n + 1)*A000166(n) + (-1)^(n+1)*(n-1)^2) / 6. %C A105928 Wang, Miska, & Mező call these 3-derangement numbers. a(n) counts the fixed point free permutations (derangements) on n + 3 elements such that the first 3 elements belong to distinct cycles. - _Istvan Mezo_, Apr 05 2017 %D A105928 P. A. MacMahon, Combinatory Analysis, 2 vols., Chelsea, NY, 1960, see p. 108. %H A105928 Vincenzo Librandi, <a href="/A105928/b105928.txt">Table of n, a(n) for n = 0..200</a> %H A105928 C.-Y. Wang, P. Miska, I. Mező, <a href="http://doi.org/10.1016/j.disc.2016.10.012">The r-derangement numbers</a>, Discrete Mathematics 340.7 (2017): 1681-1692. %F A105928 G.f.: (2*x-1)*hypergeom([1,2],[],x/(1+x))/(3*(1+x)^2) - (5*x-1)*hypergeom([2,3],[],x/(1+x))/(3*(1+x)^3). - _Mark van Hoeij_, Nov 19 2011 %F A105928 E.g.f.: x^3*exp(-x)/(1-x)^4. - _Istvan Mezo_, Apr 05 2017 %t A105928 Table[((n^3 - 4 n + 1) Subfactorial[n] + (-1)^(n + 1) (n - 1)^2)/ 6, {n, 0, 21}] (* _Michael De Vlieger_, Apr 05 2017 *) %o A105928 (PARI) s(n) = if( n<1, 1, n * s(n-1) + (-1)^n); %o A105928 a(n) = ((n^3 - 4*n + 1) * s(n) + (-1)^(n + 1) * (n - 1)^2)/6; \\ _Indranil Ghosh_, Apr 06 2017 %K A105928 nonn %O A105928 0,4 %A A105928 _N. J. A. Sloane_, Apr 27 2005