The OEIS mourns the passing of Jim Simons and is grateful to the Simons Foundation for its support of research in many branches of science, including the OEIS.
The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A271216 a(n) = 2^n floor(n/2)! 2
 1, 2, 4, 8, 32, 64, 384, 768, 6144, 12288, 122880, 245760, 2949120, 5898240, 82575360, 165150720, 2642411520, 5284823040, 95126814720, 190253629440, 3805072588800 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Number of symmetric rearrangement maps, i.e., rearrangement maps which satisfy a=a^(AI) and a^A = a^I. REFERENCES J. Burns, Counting a Class of Signed Permutations and Chord Diagrams related to DNA Rearrangement, Preprint. LINKS Table of n, a(n) for n=0..20. J. Burns, Table of Rearrangement Maps and Patterns for n = 1, 2, and 3. FORMULA a(n) = 2^n floor(n/2)! EXAMPLE For n=0 the a(0)=1 solution is { ∅ } For n=1 the a(1)=2 solutions are { +1, -1 } For n=2 the a(2)=4 solutions are { +1+2, -2-1, +2+1, -1-2 } For n=3 the a(3)=8 solutions are { +1+2+3, -3-2-1, +3-2+1, -1+2-3, +3+2+1, -1-2-3, +1-2+3, -3+2-1 } MATHEMATICA Table[2^n*Floor[n/2]!, {n, 0, 20}] CROSSREFS Cf. A000165, A271213. Sequence in context: A128055 A061285 A194810 * A102000 A165904 A192008 Adjacent sequences: A271213 A271214 A271215 * A271217 A271218 A271219 KEYWORD nonn,easy AUTHOR Jonathan Burns, Apr 13 2016 STATUS approved

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

Last modified May 24 06:28 EDT 2024. Contains 372772 sequences. (Running on oeis4.)