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 A090327 Number of rules of a context-free grammar in Chomsky normal form that generates all permutations of n symbols. 2
 1, 4, 11, 30, 83, 234, 671, 1950, 5723, 16914, 50231, 149670, 446963, 1336794, 4002191, 11990190, 35937803, 107747874, 323112551, 969075510, 2906702243, 8719058154, 26155077311, 78461037630, 235374724283, 706107395634, 2118288632471, 6354798788550 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Colin Barker, Table of n, a(n) for n = 1..1000 P. R. J. Asveld, Generating all permutations by context-free grammars in Chomsky normal form, Theoretical Computer Science 354 (2006) 118-130. Index entries for linear recurrences with constant coefficients, signature (6,-11,6). FORMULA a(n) = ceiling[ (5*3^(n-2))/2 + 2^(n-1) - 1/2 ] for n > 1. G.f.: -x*(2*x^3-2*x^2-2*x+1) / ((x-1)*(2*x-1)*(3*x-1)). - Colin Barker, Jan 15 2015 a(n) = 6*a(n-1)-11*a(n-2)+6*a(n-3) for n >= 5. - Robert Israel, Jan 15 2015 EXAMPLE S -> AD | DA | BE | EB, D -> BC | CB, E -> AC | CA, A -> a, B -> b, C-> c; so a(3)=11. MAPLE f:= gfun:-rectoproc({a(n) = 6*a(n-1)-11*a(n-2)+6*a(n-3), a(1)=1, a(2)=4, a(3)=11, a(4)=30}, a(n), 'remember'): seq(f(n), n=1..100); # Robert Israel, Jan 15 2015 MATHEMATICA f[n_] := Ceiling[5/2*3^(n - 2) + 2^(n - 1) - 1/2]; Table[ f[n], {n, 2, 27}] (* Robert G. Wilson v, Jan 30 2004 *) PROG (PARI) Vec(-x*(2*x^3-2*x^2-2*x+1)/((x-1)*(2*x-1)*(3*x-1)) + O(x^100)) \\ Colin Barker, Jan 15 2015 CROSSREFS Sequence in context: A019496 A021006 A078141 * A183118 A183125 A183123 Adjacent sequences:  A090324 A090325 A090326 * A090328 A090329 A090330 KEYWORD nonn,easy AUTHOR Peter R. J. Asveld, Jan 27 2004 EXTENSIONS More terms from Robert G. Wilson v, Jan 30 2004 STATUS approved

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Last modified October 16 12:35 EDT 2018. Contains 316263 sequences. (Running on oeis4.)