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 A308305 a(n) = s(n,n) + s(n,n-1) + s(n,n-2), where s(n,k) are the unsigned Stirling numbers of the first kind (see A132393). 2
 1, 2, 6, 18, 46, 101, 197, 351, 583, 916, 1376, 1992, 2796, 3823, 5111, 6701, 8637, 10966, 13738, 17006, 20826, 25257, 30361, 36203, 42851, 50376, 58852, 68356, 78968, 90771, 103851, 118297, 134201, 151658, 170766, 191626, 214342, 239021, 265773, 294711 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Pairwise perpendicular bisectors divide the Euclidean plane into a maximum of a(n) regions. This maximum value a(n) occurs when no three points are collinear and no four points are concyclic in the plane, and with no perpendicular bisectors parallel or coinciding [Zaslavsky, Eq. (1.1)]. This count of regions in the plane is relevant for social science applications to voting preferences based on proximity to candidates on issues. REFERENCES T. Zaslavsky, Perpendicular dissections of space. Discrete Comput. Geom. 27 (2002), no. 3, 303-351. LINKS Colin Barker, Table of n, a(n) for n = 1..1000 Alvaro Carbonero, Beth Anne Castellano, Gary Gordon, Charles Kulick, Karie Schmitz, and Brittany Shelton, Permutations of point sets in R_d, arXiv:2106.14140 [math.CO], 2021. I. J. Good and T. N. Tideman, Stirling numbers and a geometric structure from voting theory, J. Combinatorial Theory Ser. A 23 (1977), 34-45. T. Zaslavsky, Perpendicular dissections of space, arXiv:1001.4435 [math.CO], 2010. See equation (1.1) with d=2. Index entries for linear recurrences with constant coefficients, signature (5,-10,10,-5,1). FORMULA a(n) = s(n,n) + s(n,n-1) + s(n,n-2), where s(n,k) are the unsigned Stirling numbers of the first kind. a(n) = (1/24)*(24 - 14*n + 21*n^2 - 10*n^3 + 3*n^4). From Colin Barker, Jun 30 2019: (Start) G.f.: x*(1 - 3*x + 6*x^2 - 2*x^3 + x^4) / (1 - x)^5. a(n) = 5*a(n-1) - 10*a(n-2) + 10*a(n-3) - 5*a(n-4) + a(n-5) for n>5. (End) MATHEMATICA Table[(1/24)(24 - 14 i + 21 i^2 - 10 i^3 + 3 i^4), {i, 40}] PROG (Magma) [(1/24)*(24 - 14*n + 21*n^2 - 10*n^3 + 3*n^4): n in [1..40]]; // Vincenzo Librandi, Jun 30 2019 (PARI) Vec(x*(1 - 3*x + 6*x^2 - 2*x^3 + x^4) / (1 - x)^5 + O(x^40)) \\ Colin Barker, Jun 30 2019 CROSSREFS The unsigned Stirling numbers of the first kind s(n,k) are given in A132393. The division of space formulation can be generalized to higher dimensions with use of A008275 by Good and Tideman's work. The maximum number of regions generated by pairwise perpendicular bisectors on a sphere is given by A087645. Sequence in context: A120414 A251685 A341490 * A054136 A232600 A140960 Adjacent sequences:  A308302 A308303 A308304 * A308306 A308307 A308308 KEYWORD nonn,easy AUTHOR Alvaro Carbonero, Elizabeth Castellano, Charles Kulick, Karie Schmitz, Jun 05 2019 STATUS approved

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Last modified October 1 16:19 EDT 2022. Contains 357149 sequences. (Running on oeis4.)