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 A303609 a(n) = 2*n^3 + 9*n^2 + 9*n. 0
 0, 20, 70, 162, 308, 520, 810, 1190, 1672, 2268, 2990, 3850, 4860, 6032, 7378, 8910, 10640, 12580, 14742, 17138, 19780, 22680, 25850, 29302, 33048, 37100, 41470, 46170, 51212, 56608, 62370, 68510, 75040, 81972, 89318, 97090, 105300, 113960, 123082, 132678, 142760 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS y-values solving the Diophantine equation 4*x^3 + 9*x^2 = y^2 for positive x (which are listed in A028552). The equation is also satisfied by y=2 and x=-2. LINKS Index entries for linear recurrences with constant coefficients, signature (4,-6,4,-1). FORMULA G.f.: 2*x*(10 - 5*x + x^2) / (1 - x)^4. a(n) = n*(2*n^2 + 9*n + 9) = n * A014107(n+3). MATHEMATICA Table[2 n^3 + 9 n^2 + 9 n, {n, 0, 40}] (* or *) CoefficientList[Series[(20 x - 10 x^2 + 2 x^3) / (1 - x)^4, {x, 0, 33}], x] PROG (MAGMA) [2*n^3+9*n^2+9*n: n in [0..40]] (GAP) List([0..50], n->n*(2*n^2+9*n+9)); # Muniru A Asiru, Apr 29 2018 CROSSREFS Cf. A014107, A028552 (associated x). Sequence in context: A071395 A245856 A053741 * A052516 A083873 A240820 Adjacent sequences:  A303606 A303607 A303608 * A303610 A303611 A303612 KEYWORD nonn,easy AUTHOR Vincenzo Librandi, Apr 28 2018 STATUS approved

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Last modified November 19 07:20 EST 2018. Contains 317333 sequences. (Running on oeis4.)