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A316247
Decimal expansion of the middle x such that 1/x + 1/(x+1) + 1/(x+2) = 3.
4
7, 2, 2, 3, 5, 1, 7, 2, 4, 4, 6, 4, 3, 7, 6, 2, 9, 5, 1, 6, 5, 5, 0, 2, 1, 4, 9, 2, 5, 6, 4, 4, 5, 6, 6, 4, 2, 8, 7, 7, 9, 4, 9, 0, 3, 5, 9, 0, 0, 2, 8, 3, 2, 8, 9, 1, 4, 5, 3, 9, 2, 7, 3, 6, 8, 8, 0, 2, 9, 7, 8, 9, 1, 8, 1, 1, 2, 5, 9, 9, 3, 8, 4, 6, 0, 1
OFFSET
0,1
COMMENTS
Equivalently, the middle root of 3*x^3 + 6*x^2 - 2;
Least root: A316246;
Greatest root: A316248.
See A305328 for a guide to related sequences.
FORMULA
greatest root: -2/3 + (4/3)*cos((1/3)*arctan(3*sqrt(7)))
****
middle: -2/3 - (2/3)*cos((1/3)*arctan(3*sqrt(7))) + (2*sin((1/3)*arctan(3*sqrt(7))))/sqrt(3)
****
least: -2/3 - (2/3)*cos((1/3)*arctan(3*sqrt(7))) - (2*sin((1/3)*arctan(3*sqrt(7))))/sqrt(3)
EXAMPLE
greatest root: 0.5148689384387165869...
middle root: -0.7223517244643762951...
least root: -1.792517213974340291...
MATHEMATICA
a = 1; b = 1; c = 1; u = 0; v = 1; w = 2; d = 3;
r[x_] := a/(x + u) + b/(x + v) + c/(x + w);
t = x /. ComplexExpand[Solve[r[x] == d, x]]
N[t, 20]
u = N[t, 200];
RealDigits[u[[1]]] (* A316246, greatest *)
RealDigits[u[[2]]] (* A316247, least *)
RealDigits[u[[3]]] (* A316248, middle *)
CROSSREFS
KEYWORD
nonn,cons
AUTHOR
Clark Kimberling, Aug 19 2018
STATUS
approved