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 A086640 Arrange n^2 octagons that each have area 7 so that they leave (n-1)^2 square gaps each with area 2; a(n) is the total area of these polygons. 0
 7, 30, 71, 130, 207, 302, 415, 546, 695, 862, 1047, 1250, 1471, 1710, 1967, 2242, 2535, 2846, 3175, 3522, 3887, 4270, 4671, 5090, 5527, 5982, 6455, 6946, 7455, 7982, 8527, 9090, 9671, 10270, 10887, 11522, 12175, 12846, 13535, 14242, 14967, 15710 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 REFERENCES Keith Devlin, "The language of mathematics", Henry Holt, NY, plate 9 after p. 249. LINKS Index entries for linear recurrences with constant coefficients, signature (3,-3,1). FORMULA a(n) = 9n^2-4n+2. G.f. -x*(2*x+7)*(1+x) / (x-1)^3 . - R. J. Mathar, Sep 15 2012 PROG (PARI) a(n)=9*n^2-4*n+2 \\ Charles R Greathouse IV, Jun 17 2017 CROSSREFS Sequence in context: A063148 A116283 A139274 * A083474 A030440 A256225 Adjacent sequences:  A086637 A086638 A086639 * A086641 A086642 A086643 KEYWORD nonn,easy,less AUTHOR Jun Mizuki (suzuki32(AT)sanken.osaka-u.ac.jp), Jul 26 2003 EXTENSIONS Edited and extended by David Wasserman, Jun 20 2007 STATUS approved

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Last modified August 13 04:54 EDT 2020. Contains 336442 sequences. (Running on oeis4.)