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 A209916 Kolmogorov's button, 2-color generic convex polygon version. 0
 0, 0, 2, 26, 1457, 1889567, 470184984575, 359414999291950792703, 27008149481218253520093899825086463, 12768639440249474099578561928613102801011591209543532543 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS This sequence shows the number of distinct patterns that can be created with threads of 2 colors while sewing on a button with n buttonholes located on the vertices of a generic convex n-gon, i.e., a convex n-gon with no more than two diagonals intersecting at any point in its interior. The number of all distinct patterns due to intersections made by differently colored diagonals of the n-gon, equaling 2^A000332(n), is taken into account (as red-diagonal-over-green-diagonal, for instance, is a different pattern from green-diagonal-over-red-diagonal). In general, if the number of colors is c, then a(n) = ((c+1)^(n-1)*n/2)*((c-1)*c)^A000332(n)-1. Kolmogorov's button problem is briefly mentioned in the book by Gessen. REFERENCES Masha Gessen, Perfect Rigor, A Genius and the Mathematical Breakthrough of the Century, Houghton Mifflin Harcourt, 2009, page 38. LINKS FORMULA a(n) = A047656(n)*2^A000332(n) - 1. EXAMPLE For the classic 4-hole button (where n=4 and c=2) the number of distinct patterns is a(n) = A047656(4)*2^A000332(4) - 1 = 729*2 - 1 = 1457. The "-1" stands for the case where the threads are missing, i.e., where the button is unattached to the cloth. MATHEMATICA Table[-1+(3^Binomial[n, 2])*(2^Binomial[n, 4]), {n, 0, 9}] (* Ivan N. Ianakiev, Dec 29 2015 *) PROG (MAGMA) [3^((n^2-n) div 2)*2^Binomial(n, 4)-1: n in [0..10]]; // Vincenzo Librandi, Dec 29 2015 CROSSREFS Cf. A000332, A047656. Sequence in context: A002704 A015215 A158120 * A156213 A159318 A318132 Adjacent sequences:  A209913 A209914 A209915 * A209917 A209918 A209919 KEYWORD easy,nonn AUTHOR Ivan N. Ianakiev, Mar 15 2012 STATUS approved

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Last modified May 19 17:48 EDT 2019. Contains 323395 sequences. (Running on oeis4.)