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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
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.
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: A335557 A245856 A053741 * A052516 A083873 A240820
KEYWORD
nonn,easy
AUTHOR
Vincenzo Librandi, Apr 28 2018
STATUS
approved