%I A080049
%S A080049 0,2,11,63,388,2734,21893,197069,1970726,21678036,260136487,3381774403,
%T A080049 47344841720,710172625898,11362762014473,193166954246169,
%U A080049 3477005176431178,66063098352192544,1321261967043851051
%N A080049 Operation count to create all permutations of n distinct elements using 
               Algorithm L (lexicographic permutation generation) from Knuth's The 
               Art of Computer Programming, Vol. 4, chapter 7.2.1.2. Sequence gives 
               number of interchange operations in step L4.
%D A080049 D. E. Knuth: The Art of Computer Programming, Volume 4, Combinatorial 
               Algorithms, Volume 4A, Enumeration and Backtracking. Pre-fascicle 
               2B, A draft of section 7.2.1.2: Generating all permutations. Available 
               online; see link.
%D A080049 R. J. Ord-Smith: Generation of permutation sequences: Part 1 The Computer 
               Journal Volume 13, Number 2 May 1970. pp. 152-155. See link
%H A080049 D. E. Knuth, <a href="http://www-cs-faculty.stanford.edu/~knuth/fasc2b.ps.gz">
               TAOCP Vol. 4, Pre-fascicle 2b (generating all permutations)</a>.
%H A080049 R. J. Ord-Smith, <a href="http://www3.oup.co.uk/jnls/list/computer_journal/
               hdb/Volume_13/Issue_02/default.html">Generation of permutation sequences</
               a>
%H A080049 Hugo Pfoertner, <a href="http://www.randomwalk.de/sequences/lpure.txt">
               FORTRAN implementation of Knuth's Algorithm L for lexicographic permutation 
               generation</a>.
%F A080049 a(2)=0, a(n)=n*a(n-1) + (n-1)*floor[(n-1)/2] c = limit n ->infinity a(n)/
               n! = 0.5430806.. = (e+1/e)/2-1 a(n) = floor [c*n! - (n-1)/2] for 
               n>=2
%o A080049 FORTRAN program available at Pfoertner link
%Y A080049 Cf. A080047, A080048, A038155, A038156, A056542, A079756.
%Y A080049 Sequence in context: A002629 A065928 A114175 this_sequence A126745 A038725 
               A161947
%Y A080049 Adjacent sequences: A080046 A080047 A080048 this_sequence A080050 A080051 
               A080052
%K A080049 nonn
%O A080049 2,2
%A A080049 Hugo Pfoertner (hugo(AT)pfoertner.org), Jan 24 2003