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A115451 Expansion of 1/((1+x)*(1-2*x)*(1+x^2)). 6
1, 1, 2, 4, 9, 17, 34, 68, 137, 273, 546, 1092, 2185, 4369, 8738, 17476, 34953, 69905, 139810, 279620, 559241, 1118481, 2236962, 4473924, 8947849, 17895697, 35791394, 71582788, 143165577, 286331153, 572662306, 1145324612, 2290649225, 4581298449, 9162596898 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

Signed version is A077931. Row sums of A115450.

LINKS

G. C. Greubel, Table of n, a(n) for n = 0..1000

Index entries for linear recurrences with constant coefficients, signature (1,1,1,2).

FORMULA

a(n) = a(n-1) + a(n-2) + a(n-3) + 2*a(n-4);

a(n) = Sum_{k=0..n} (2^(n-k+1)-1)(-1)^k} - Sum_{k=0..floor(n/2)} (2^(n-2k)-1)(-1)^k}.

a(n) = A000975(n+1) - A077854(n-1).

a(n) = A112030(n)/10 + (-1)^n/6 +2^(n+3)/15. - R. J. Mathar, Feb 06 2011

MATHEMATICA

CoefficientList[Series[1/((1 + x) (1 - 2 x) (1 + x^2)), {x, 0, 50}], x] (* Vladimir Joseph Stephan Orlovsky, Jun 20 2011 *)

LinearRecurrence[{1, 1, 1, 2}, {1, 1, 2, 4}, 50] (* Harvey P. Dale, Oct 22 2011 *)

PROG

(PARI) x='x+O('x^50); Vec(1/((1+x)*(1-2*x)*(1+x^2))) \\ G. C. Greubel, Sep 26 2017

CROSSREFS

Sequence in context: A088039 A266108 A077931 * A245122 A291728 A268649

Adjacent sequences:  A115448 A115449 A115450 * A115452 A115453 A115454

KEYWORD

easy,nonn

AUTHOR

Paul Barry, Jan 22 2006

STATUS

approved

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Last modified October 23 04:31 EDT 2018. Contains 316519 sequences. (Running on oeis4.)