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 A195032 Vertex number of a square spiral in which the length of the first two edges are the legs of the primitive Pythagorean triple [5, 12, 13]. The edges of the spiral have length A195031. 6
 0, 5, 17, 27, 51, 66, 102, 122, 170, 195, 255, 285, 357, 392, 476, 516, 612, 657, 765, 815, 935, 990, 1122, 1182, 1326, 1391, 1547, 1617, 1785, 1860, 2040, 2120, 2312, 2397, 2601, 2691, 2907, 3002, 3230, 3330, 3570, 3675, 3927, 4037, 4301, 4416, 4692 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Zero together with partial sums of A195031. The spiral contains infinitely many Pythagorean triples in which the hypotenuses on the main diagonal are the positives multiples of 13 (cf. A008595). The vertices on the main diagonal are the numbers A195037 = (5+12)*A000217 = 17*A000217, where both 5 and 12 are the first two edges in the spiral. The distance "a" between nearest edges that are perpendicular to the initial edge of the spiral is 5, while the distance "b" between nearest edges that are parallel to the initial edge is 12, so the distance "c" between nearest vertices on the same axis is 13 because from the Pythagorean theorem we can write c = (a^2 + b^2)^(1/2) = sqrt(5^2 + 12^2) = sqrt(25 + 144) = sqrt(169) = 13. - Omar E. Pol, Oct 12 2011 LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..10000 Ron Knott, Pythagorean triangles and Triples Eric Weisstein's World of Mathematics, Pythagorean Triple Index entries for linear recurrences with constant coefficients, signature (1,2,-2,-1,1). FORMULA From Bruno Berselli, Oct 13 2011:  (Start) G.f.: x*(5 + 12*x)/((1 + x)^2*(1 - x)^3). a(n) = (1/2)*((2*n + (-1)^n + 3)/4)*((34*n - 3*(-1)^n+3)/4) = (2*n*(17*n + 27) + (14*n - 3)*(-1)^n + 3)/16. a(n) = a(n-1) + 2*a(n-2) - 2*a(n-3) - a(n-4) + a(n-5). (End) E.g.f.: (1/16)*((3 + 88*x + 34*x^2)*exp(x) - (3 + 14*x)*exp(-x)). - Franck Maminirina Ramaharo, Nov 23 2018 MATHEMATICA a[n_] := (2 n (17 n + 27) + (14 n - 3)*(-1)^n + 3)/16; Array[a, 50, 0] (* Amiram Eldar, Nov 23 2018 *) PROG (MAGMA) [(2*n*(17*n+27)+(14*n-3)*(-1)^n+3)/16: n in [0..50]]; // Vincenzo Librandi, Oct 14 2011 (PARI) vector(50, n, n--; (2*n*(17*n+27)+(14*n-3)*(-1)^n+3)/16) \\ G. C. Greubel, Nov 23 2018 (Sage) [(2*n*(17*n+27)+(14*n-3)*(-1)^n+3)/16 for n in range(50)] # G. C. Greubel, Nov 23 2018 CROSSREFS Cf. A195020, A195031, A195034, A195036, A195037. Sequence in context: A268526 A018447 A196142 * A264618 A271471 A217512 Adjacent sequences:  A195029 A195030 A195031 * A195033 A195034 A195035 KEYWORD nonn,easy AUTHOR Omar E. Pol, Sep 12 2011 STATUS approved

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Last modified November 22 10:59 EST 2019. Contains 329389 sequences. (Running on oeis4.)