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 A036999 Restricted permutations. (Formerly N1692) 2
 6, 9, 12, 18, 27, 42, 66, 105, 168, 270, 435, 702, 1134, 1833, 2964, 4794, 7755, 12546, 20298, 32841, 53136, 85974, 139107, 225078, 364182, 589257, 953436, 1542690, 2496123, 4038810, 6534930, 10573737, 17108664, 27682398, 44791059 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 REFERENCES N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (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. FORMULA 3*A000381. G.f.: 3*(2-x-2*x^2)/((x^2+x-1)*(x-1)). - Vincenzo Librandi, Jul 01 2017 MATHEMATICA Join[{6}, Table[3 Fibonacci[n+3] + 3, {n, 0, 40}]] (* or *) CoefficientList[Series[3 (2 - x - 2 x^2) / ((x^2 + x - 1) (x - 1)), {x, 0, 33}], x] (* Vincenzo Librandi, Jul 01 2017 *) PROG (MAGMA) [6] cat [3*Fibonacci(n+3)+3: n in [0..40]]; // Vincenzo Librandi, Jul 01 2017 CROSSREFS Equals A022086(n+3) + 3. Sequence in context: A245685 A114554 A023386 * A290130 A118782 A246356 Adjacent sequences:  A036996 A036997 A036998 * A037000 A037001 A037002 KEYWORD nonn AUTHOR STATUS approved

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