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 A080048 #11 Sep 02 2025 10:58:39 %S A080048 1,7,34,182,1107,7773,62212,559948,5599525,61594835,739138086, %T A080048 9608795202,134523132919,2017846993897,32285551902472,548854382342168, %U A080048 9879378882159177,187708198761024543,3754163975220491050 %N A080048 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 loop repetitions in reversal step. %D A080048 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. %H A080048 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 A080048 <a href="http://www.randomwalk.de/sequences/lpure.txt">FORTRAN implementation of Knuth's Algorithms L for lexicographic permutation generation</a>. %F A080048 a(2)=1, a(n)=n*a(n-1) + (n-1)*floor[(n+1)/2] for n>=3. %F A080048 c = limit n --> infinity a(n)/n! = 1.54308063481524377826 = (e+1/e)/2, a(n) = floor [c*n!-(n+1)/2] for n>=2. %o A080048 (Fortran) ! Program available at link. %Y A080048 Cf. A038155, A038156, A056542, A080047, A080049, A079755. %K A080048 nonn,changed %O A080048 2,2 %A A080048 _Hugo Pfoertner_, Jan 24 2003