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 A296910 a(0)=1, a(1)=4; thereafter a(n) = 4*n-2*(-1)^n. 39
 1, 4, 6, 14, 14, 22, 22, 30, 30, 38, 38, 46, 46, 54, 54, 62, 62, 70, 70, 78, 78, 86, 86, 94, 94, 102, 102, 110, 110, 118, 118, 126, 126, 134, 134, 142, 142, 150, 150, 158, 158, 166, 166, 174, 174, 182, 182, 190, 190, 198, 198, 206, 206, 214, 214, 222, 222, 230, 230, 238, 238 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Coordination sequence for the bew tiling with respect to a point where two hexagons meet at only a single point. The coordination sequence for the other type of point can be shown to be A008574. Notes: There is one point on the positive x-axis at edge-distance n from the origin iff n is even; there is one point on the positive y-axis at edge-distance n from the origin iff n>1 is odd; and the number of points inside the first quadrant at distance n from 0 is n if n is odd, and n-1 if n is even. Then a(n) = 2*(number on positive x-axis + number on positive y-axis) + 4*(number in interior of first quadrant). LINKS Colin Barker, Table of n, a(n) for n = 0..1000 Brian Galebach, k-uniform tilings (k <= 6) and their A-numbers C. Goodman-Strauss and N. J. A. Sloane, A Coloring Book Approach to Finding Coordination Sequences, arXiv:1803.08530, March 2018. Reticular Chemistry Structure Resource (RCSR), The bew tiling (or net) N. J. A. Sloane, Illustration of initial terms. Points in the first quadrant are marked with their edge-distance from the origin (the heavy black circle). (Ignore the black rectangles, which show some fundamental cells for this tiling.) Index entries for linear recurrences with constant coefficients, signature (1,1,-1). FORMULA From Colin Barker, Dec 23 2017: (Start) G.f.: (1 + 3*x + x^2 + 5*x^3 - 2*x^4) / ((1 - x)^2*(1 + x)). a(n) = a(n-1) + a(n-2) - a(n-3) for n>4. (End) MATHEMATICA {1, 4}~Join~Array[4 # - 2 (-1)^# &, 59, 2] (* or *) LinearRecurrence[{1, 1, -1}, {1, 4, 6, 14, 14}, 61] (* or *) CoefficientList[Series[(1 + 3 x + x^2 + 5 x^3 - 2 x^4)/((1 - x)^2*(1 + x)), {x, 0, 60}], x] (* Michael De Vlieger, Dec 23 2017 *) PROG (PARI) Vec((1 + 3*x + x^2 + 5*x^3 - 2*x^4) / ((1 - x)^2*(1 + x)) + O(x^50)) \\ Colin Barker, Dec 23 2017 CROSSREFS Apart from first two terms, same as A168384. Cf. A008574. See A296911 for partial sums. Coordination sequences for the 20 2-uniform tilings in the order in which they appear in the Galebach catalog, together with their names in the RCSR database (two sequences per tiling): #1 krt A265035, A265036; #2 cph A301287, A301289; #3 krm A301291, A301293; #4 krl A301298, A298024; #5 krq A301299, A301301; #6 krs A301674, A301676; #7 krr A301670, A301672; #8 krk A301291, A301293; #9 krn A301678, A301680; #10 krg A301682, A301684; #11 bew A008574, A296910; #12 krh A301686, A301688; #13 krf A301690, A301692; #14 krd A301694, A219529; #15 krc A301708, A301710; #16 usm A301712, A301714; #17 krj A219529, A301697; #18 kre A301716, A301718; #19 krb A301720, A301722; #20 kra A301724, A301726. Sequence in context: A253535 A310601 A310602 * A310603 A310604 A310605 Adjacent sequences:  A296907 A296908 A296909 * A296911 A296912 A296913 KEYWORD nonn,easy AUTHOR N. J. A. Sloane, Dec 22 2017 STATUS approved

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Last modified January 19 15:53 EST 2019. Contains 319307 sequences. (Running on oeis4.)