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 A256456 Number of simple 2n-gons with only right angles, disregarding edge lengths. 1
 0, 1, 1, 4, 8, 29, 79, 280, 912, 3260, 11410, 41272, 148976, 544802, 1997499, 7372080, 27299360, 101520714, 378721134, 1417339352, 5318837680, 20012141478, 75473438326, 285268537424, 1080433781728, 4099860518208, 15585111068644, 59343308199216, 226312777319776 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,4 COMMENTS a(n) is also the number of bracelets containing n+2 R's and n-2 L's. This is also the number of bracelets of n-2 nonnegative integers whose sum is n+2; this explains the labels on the decagons in the illustration. - Mark Jason Dominus, Jun 08 2015 LINKS Bjarki Ágúst Guðmundsson, Table of n, a(n) for n = 1..100 [Terms 1 through 30 were computed by Brent A. Yorgey; and terms 31 to 100 by Bjarki Ágúst Guðmundsson, Jul 07 2016] Mark Jason Dominus, Examples of the a(5)=8 orthogonal decagons; also bracelets of 7 R's and 3 L's Mark Dominus, Perl program Brent Yorgey, Haskell program EXAMPLE For n=5 the a(5)=8 bracelets are RRRLRRLRRL, RRRLRRRLRL, RRRRLRRLRL, RRRRLRRRLL, RRRRRLRLRL, RRRRRLRRLL, RRRRRRLRLL, RRRRRRRLLL. MATHEMATICA {0}~Join~Table[Coefficient[CycleIndexPolynomial[DihedralGroup[2n], Table[1+t^i, {i, 1, 2n}]], t^(n+2)], {n, 2, 30}] (* Bjarki Ágúst Guðmundsson, Jul 07 2016 *) CROSSREFS Sequence in context: A300461 A280085 A297638 * A270522 A317583 A020331 Adjacent sequences:  A256453 A256454 A256455 * A256457 A256458 A256459 KEYWORD nonn AUTHOR Mark Jason Dominus, Mar 29 2015 EXTENSIONS Corrected (a(14) was wrong) and extended by Brent A. Yorgey, Dec 11 2015 a(31)-a(100) from Bjarki Ágúst Guðmundsson, Jul 07 2016 STATUS approved

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Last modified December 10 00:30 EST 2018. Contains 318032 sequences. (Running on oeis4.)