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A238236 Expansion of (1-x-x^2)/((x-1)*(x^3+3*x^2+2*x-1)). 3
1, 2, 6, 18, 55, 169, 520, 1601, 4930, 15182, 46754, 143983, 443409, 1365520, 4205249, 12950466, 39882198, 122821042, 378239143, 1164823609, 3587185688, 11047081345, 34020543362, 104769516446, 322647744322, 993624581343, 3059961912097, 9423445312544 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Row sums of the triangle in A152440.

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..200

FORMULA

G.f.: (1-x-x^2)/(1-3*x-x^2+2*x^3+x^4).

a(n) = 3*a(n-1) + a(n-2) -2*a(n-3) - a(n-4), a(0) = 1, a(1) = 2, a(2) = 6, a(3) = 18.

a(n) = A097472(n) - A097472(n-1) - A097472(n-2).

a(n) = A060945(2*n).

MATHEMATICA

CoefficientList[Series[(1 - x - x^2)/(1 - 3 x - x^2 + 2 x^3 + x^4), {x, 0, 40}], x ](* Vincenzo Librandi, Feb 22 2014 *)

CROSSREFS

Cf. A097472, A152440.

Sequence in context: A148455 A094590 A004529 * A294159 A000778 A006725

Adjacent sequences:  A238233 A238234 A238235 * A238237 A238238 A238239

KEYWORD

nonn

AUTHOR

Philippe Deléham, Feb 20 2014

STATUS

approved

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Last modified January 26 11:26 EST 2020. Contains 331279 sequences. (Running on oeis4.)