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 A258129 Octagonal numbers (A000567) that are the sum of three consecutive octagonal numbers. 5
 698901, 5102520783381, 37252493940331837461, 271973082264557457061125141, 1985621622943208359132836202790421, 14496630316026749501691464257547633057301, 105837027604506739193825102426073141683789429781, 772695182809023513889440668692977953487035688873891861 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Colin Barker, Table of n, a(n) for n = 1..145 Index entries for linear recurrences with constant coefficients, signature (7300803,-7300803,1). FORMULA G.f.: -21*x*(x^2 -844482*x +33281)/((x-1)*(x^2 -7300802*x +1)). EXAMPLE 698901 is in the sequence because Oct(483) = 698901 = 231296 + 232965 + 234640 = Oct(278) + Oct(279) + Oct(280). MATHEMATICA CoefficientList[Series[-21*x*(x^2 -844482*x +33281)/((x-1)*(x^2 -7300802*x +1)), {x, 0, 50}], x] (* G. C. Greubel, Oct 18 2017 *) LinearRecurrence[{7300803, -7300803, 1}, {698901, 5102520783381, 37252493940331837461}, 20] (* Harvey P. Dale, Sep 16 2018 *) PROG (PARI) Vec(-21*x*(x^2 -844482*x +33281)/((x-1)*(x^2 -7300802*x +1)) + O('x^20)) CROSSREFS Cf. A000567, A258128, A258130, A258131, A258132. Sequence in context: A205608 A205439 A027829 * A204496 A332850 A183835 Adjacent sequences:  A258126 A258127 A258128 * A258130 A258131 A258132 KEYWORD nonn,easy AUTHOR Colin Barker, May 21 2015 STATUS approved

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Last modified December 1 22:12 EST 2021. Contains 349435 sequences. (Running on oeis4.)