This site is supported by donations to The OEIS Foundation.

 Annual appeal: Please make a donation to keep the OEIS running! Over 6000 articles have referenced us, often saying "we discovered this result with the help of the OEIS". Other ways to donate

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A000496 Restricted permutations. (Formerly M5143 N2231) 2
 1, 1, 2, 6, 24, 44, 80, 144, 260, 476, 872, 1600, 2940, 5404, 9936, 18272, 33604, 61804, 113672, 209072, 384540, 707276, 1300880, 2392688, 4400836, 8094396, 14887912, 27383136, 50365436, 92636476, 170385040, 313386944, 576408452, 1060180428, 1949975816, 3586564688 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 REFERENCES N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence). N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..1000 N. S. Mendelsohn, Permutations with confined displacement, Canad. Math. Bull., 4 (1961), 29-38. Simon Plouffe, Approximations de séries génératrices et quelques conjectures, Dissertation, Université du Québec à Montréal, 1992. Simon Plouffe, 1031 Generating Functions and Conjectures, Université du Québec à Montréal, 1992. MAPLE A000496:=-4*(-6+z+2*z**2+4*z**3+z**4)/(z-1)/(z**3+z**2+z-1); # [Conjectured by Simon Plouffe in his 1992 dissertation.] a:= n-> if n<4 then 0 elif n=4 then 24 else (Matrix([[8, 12, 4, 0]]). Matrix(4, (i, j)-> if (i=j-1) then 1 elif j=1 then [2, 0, 0, -1][i] else 0 fi)^n)[1, 3] fi: seq (a(n), n=4..40); # Alois P. Heinz, Aug 26 2008 MATHEMATICA a[n_] := Switch[n, 0, 1, 1, 1, 2, 2, 3, 6, 4, 24, _, ({8, 12, 4, 0} . MatrixPower[Table[Which[i == j-1, 1, j == 1, {2, 0, 0, -1}[[i]], True, 0], {i, 1, 4}, {j, 1, 4}], n])[[3]]]; Table[a[n], {n, 0, 40}] (* Jean-François Alcover, Mar 12 2014, after Alois P. Heinz *) CROSSREFS Sequence in context: A067653 A090755 A192196 * A004306 A092485 A113904 Adjacent sequences:  A000493 A000494 A000495 * A000497 A000498 A000499 KEYWORD nonn AUTHOR STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.