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 A085250 4 times hexagonal numbers: a(n) = 4*n*(2*n-1). 23
 0, 4, 24, 60, 112, 180, 264, 364, 480, 612, 760, 924, 1104, 1300, 1512, 1740, 1984, 2244, 2520, 2812, 3120, 3444, 3784, 4140, 4512, 4900, 5304, 5724, 6160, 6612, 7080, 7564, 8064, 8580, 9112, 9660, 10224, 10804, 11400, 12012, 12640, 13284 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS a(n) also can represented as n concentric squares (see example). - Omar E. Pol, Aug 21 2011 Sequence found by reading the line from 0, in the direction 0, 4, ..., in the square spiral whose vertices are the triangular numbers A000217. - Omar E. Pol, Sep 03 2011 LINKS Ivan Panchenko, Table of n, a(n) for n = 0..1000 Index entries for linear recurrences with constant coefficients, signature (3,-3,1). FORMULA a(n) = A067239(n)/2, for n>0. Sum_{n>0} 1/a(n) = log(2)/2. a(n) = A000384(n)*4. - Omar E. Pol, Dec 11 2008 a(n) = 16*n + a(n-1) - 12 (with a(0)=0). - Vincenzo Librandi, Aug 08 2010 G.f.: 4*x*(1 + 3*x)/(1 - 3*x + 3*x^2 - x^3). - Colin Barker, Jan 04 2012 E.g.f.: 4*x*(2*x + 1)*exp(x). - G. C. Greubel, Jul 14 2017 a(n) = A046092(2n-1), for n > 0. - Bruce J. Nicholson, Sep 04 2017 EXAMPLE From Omar E. Pol, Aug 21 2011: (Start) Illustration of initial terms as concentric squares: . .                           o o o o o o o o o o .                           o                 o .            o o o o o o    o   o o o o o o   o .            o         o    o   o         o   o .     o o    o   o o   o    o   o   o o   o   o .     o o    o   o o   o    o   o   o o   o   o .            o         o    o   o         o   o .            o o o o o o    o   o o o o o o   o .                           o                 o .                           o o o o o o o o o o . .      4          24                 60 . (End) MATHEMATICA Table[8*n^2 - 4*n, {n, 0, 50}] (* G. C. Greubel, Jul 14 2017 *) PROG (PARI) a(n)=4*n*(2*n-1) \\ Charles R Greathouse IV, Sep 24 2015 CROSSREFS Cf. A067239, A000384, A033581, A046092, A152734, A152751, A194274. Sequence in context: A191778 A157625 A128205 * A166870 A124350 A112611 Adjacent sequences:  A085247 A085248 A085249 * A085251 A085252 A085253 KEYWORD nonn,easy AUTHOR Gary W. Adamson, Jun 23 2003 EXTENSIONS Edited by Don Reble, Nov 13 2005 Added zero, better definition, corrected offset and edited original formula. - Omar E. Pol, Dec 11 2008 STATUS approved

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Last modified August 21 05:36 EDT 2019. Contains 326162 sequences. (Running on oeis4.)