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 A195314 Centered 28-gonal numbers. 6
 1, 29, 85, 169, 281, 421, 589, 785, 1009, 1261, 1541, 1849, 2185, 2549, 2941, 3361, 3809, 4285, 4789, 5321, 5881, 6469, 7085, 7729, 8401, 9101, 9829, 10585, 11369, 12181, 13021, 13889, 14785, 15709, 16661, 17641, 18649, 19685, 20749, 21841, 22961, 24109 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Sequence found by reading the line from 1, in the direction 1, 29, ..., in the square spiral whose vertices are the generalized enneagonal numbers A118277. Semi-axis opposite to A144555 in the same spiral. LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..10000 Index entries for linear recurrences with constant coefficients, signature (3,-3,1). FORMULA a(n) = 14*n^2 - 14*n + 1. G.f.: -x*(1 + 26*x + x^2) / (x-1)^3. - R. J. Mathar, Sep 18 2011 a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3). - Harvey P. Dale, Oct 01 2011 Sum_{n>=1} 1/a(n) = Pi*tan(sqrt(5/7)*Pi/2)/(2*sqrt(35)). - Amiram Eldar, Feb 11 2022 MATHEMATICA Table[14n^2-14n+1, {n, 50}] (* or *) LinearRecurrence[{3, -3, 1}, {1, 29, 85}, 50] PROG (Magma) [(14*n^2-14*n+1): n in [1..50]]; // Vincenzo Librandi, Sep 19 2011 (PARI) a(n)=14*n^2-14*n+1 \\ Charles R Greathouse IV, Oct 07 2015 CROSSREFS Bisection of A195145. Cf. A003154, A069129, A069133, A069190, A195315, A195316, A195317, A195318. Sequence in context: A343683 A255187 A273362 * A323218 A124784 A126383 Adjacent sequences:  A195311 A195312 A195313 * A195315 A195316 A195317 KEYWORD nonn,easy AUTHOR Omar E. Pol, Sep 16 2011 STATUS approved

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Last modified May 25 09:45 EDT 2022. Contains 354066 sequences. (Running on oeis4.)