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A106392 Expansion of 1/(1 - 6*x + 10*x^2). 3
1, 6, 26, 96, 316, 936, 2456, 5376, 7696, -7584, -122464, -658944, -2729024, -9784704, -31417984, -90660864, -229785344, -472103424, -534767104, 1512431616, 14422260736, 71409248256, 284232882176, 991304810496, 3105500041216, 8719952142336, 21264712441856, 40388753227776 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

In general, the sequence with g.f. 1/(1-2r*x+(r^2+1)*x^2)=1/((1-r*x)^2+x^2) has a(n) = Sum_{k=0..floor(n/2)} binomial(n-k,k)(r^2-1)^k*(2r)^(n-2k); a(n) = Sum_{k=0..floor((n+1)/2)} binomial(n+1,2k+1)(-1)^k*r^(n-2k).

LINKS

Robert Israel, Table of n, a(n) for n = 0..1997

Index entries for linear recurrences with constant coefficients, signature (6,-10).

FORMULA

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

a(n) = Sum_{k=0..floor(n/2)} binomial(n-k, k)(-10)^k*6^(n-2k).

a(n) = Sum_{k=0..floor((n+1)/2)} binomial(n+1, 2k+1)(-1)^k*3^(n-2k).

a(n) = 6*a(n-1) - 10*a(n-2), n>=2. - Vincenzo Librandi, Mar 22 2011

a(n) = Im((3+i)^(n+1)), where i=sqrt(-1). - César Eliud Lozada, Sep 19 2012

E.g.f.: (3*sin(x) + cos(x))*exp(3*x). - Ilya Gutkovskiy, Nov 25 2016

MAPLE

f:= gfun:- rectoproc({a(n+2)=6*a(n+1)-10*a(n), a(0)=1, a(1)=6}, a(n), remember):

map(f, [$0..50]); # Robert Israel, Nov 25 2016

MATHEMATICA

Join[{a=1, b=6}, Table[c=6*b-10*a; a=b; b=c, {n, 60}]] (* Vladimir Joseph Stephan Orlovsky, Jan 18 2011 *)

CoefficientList[Series[1/(1-6x+10x^2), {x, 0, 30}], x] (* or *) LinearRecurrence[ {6, -10}, {1, 6}, 30] (* Harvey P. Dale, Feb 05 2015 *)

PROG

(Sage) [lucas_number1(n, 6, 10) for n in xrange(1, 29)] # Zerinvary Lajos, Apr 22 2009

(PARI) imag((3+I)^(n+1)); /* Joerg Arndt, Sep 20 2012 */

(PARI) x='x+O('x^100); Vec(1/((1-3*x)^2+x^2)) \\ Altug Alkan, Dec 24 2015

CROSSREFS

Sequence in context: A036638 A036645 A000393 * A143132 A055589 A318947

Adjacent sequences:  A106389 A106390 A106391 * A106393 A106394 A106395

KEYWORD

easy,sign

AUTHOR

Paul Barry, May 01 2005

STATUS

approved

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Last modified March 22 17:25 EDT 2019. Contains 321422 sequences. (Running on oeis4.)