A016029 -id:A016029 - cp's OEIS frontend

A113405 Expansion of x^3/(1 - 2x + x^3 - 2x^4) = x^3/( (1-2x)(1+x)*(1-x+x^2) ).

0, 0, 0, 1, 2, 4, 7, 14, 28, 57, 114, 228, 455, 910, 1820, 3641, 7282, 14564, 29127, 58254, 116508, 233017, 466034, 932068, 1864135, 3728270, 7456540, 14913081, 29826162, 59652324, 119304647, 238609294, 477218588, 954437177, 1908874354, 3817748708

Offset: 0

Paul Barry, Oct 28 2005

A transform of the Jacobsthal numbers. A059633 is the equivalent transform of the Fibonacci numbers.
Paul Curtz, Aug 05 2007, observes that the inverse binomial transform of 0,0,0,1,2,4,7,14,28,57,114,228,455,910,1820,... gives the same sequence up to signs. That is, the extended sequence is an eigensequence for the inverse binomial transform (an autosequence).
The round() function enables the closed (non-recurrence) formula to take a very simple form: see Formula section. This can be generalized without loss of simplicity to a(n) = round(b^n/c), where b and c are very small, incommensurate integers (c may also be an integer fraction). Particular choices of small integers for b and c produce a number of well-known sequences which are usually defined by a recurrence - see Cross Reference. - Ross Drewe, Sep 03 2009

Vincenzo Librandi, Table of n, a(n) for n = 0..1000
M. Bernstein and N. J. A. Sloane, Some canonical sequences of integers, arXiv:math/0205301 [math.CO], 2002. [Link to arXiv version]
M. Bernstein and N. J. A. Sloane, Some canonical sequences of integers, Linear Alg. Applications, 226-228 (1995), 57-72; erratum 320 (2000), 210. [Link to Lin. Alg. Applic. version together with omitted figures]
N. J. A. Sloane, Transforms
Index entries for linear recurrences with constant coefficients, signature (2,0,-1,2).

From Ross Drewe, Sep 03 2009: (Start)
Other sequences a(n) = round(b^n / c), where b and c are very small integers:
A001045 b = 2; c = 3
A007910 b = 2; c = 5
A016029 b = 2; c = 5/3
A077947 b = 2; c = 7
abs(A078043) b = 2; c = 7/3
A007051 b = 3; c = 2
A015518 b = 3; c = 4
A034478 b = 5; c = 2
A003463 b = 5; c = 4
A015531 b = 5; c = 6
(End)

[Round(2^n/9): n in [0..40]]; // Vincenzo Librandi, Aug 11 2011

A010892 := proc(n) op((n mod 6)+1,[1,1,0,-1,-1,0]) ; end proc:
A113405 := proc(n) (2^n-(-1)^n)/9 -A010892(n-1)/3; end proc: # R. J. Mathar, Dec 17 2010

CoefficientList[Series[x^3/(1-2x+x^3-2x^4),{x,0,40}],x] (* or *) LinearRecurrence[{2,0,-1,2},{0,0,0,1},40] (* Harvey P. Dale, Apr 30 2011 *)

a(n)=2^n\/9 \\ Charles R Greathouse IV, Jun 05 2011

def A113405(n): return ((1<Chai Wah Wu, Apr 17 2025

a(n) = 2a(n-1) - a(n-3) + 2a(n-4).
a(n) = Sum_{k=0..floor(n/2)} binomial(n-k,k)*A001045(k).
a(n) = Sum_{k=0..n} binomial((n+k)/2,k)*A001045((n-k)/2)*(1+(-1)^(n-k))/2.
a(3n) = A015565(n), a(3n+1) = 2*A015565(n), a(3n+2) = 4*A015565(n). - Paul Curtz, Nov 30 2007
From Paul Curtz, Dec 16 2007: (Start)
a(n+1) - 2a(n) = A131531(n).
a(n) + a(n+3) = 2^n. (End)
a(n) = round(2^n/9). - Ross Drewe, Sep 03 2009
9*a(n) = 2^n + (-1)^n - 3*A010892(n). - R. J. Mathar, Mar 24 2018

Edited by N. J. A. Sloane, Dec 13 2007

A135541 a(n) = 2a(n-1) - a(n-2) + 2a(n-3), with a(0) = 2, a(1) = 2.

Original entry on oeis.org

0, 2, 7, 12, 21, 44, 91, 180, 357, 716, 1435, 2868, 5733, 11468, 22939, 45876, 91749, 183500, 367003, 734004, 1468005, 2936012, 5872027, 11744052, 23488101, 46976204, 93952411, 187904820, 375809637, 751619276, 1503238555, 3006477108

Offset: 0

Paul Curtz, Feb 22 2008

Vincenzo Librandi, Table of n, a(n) for n = 0..1000
Index entries for linear recurrences with constant coefficients, signature (2,-1,2).

Cf. A007909, A007910, A010712, A016029, A134658.

I:=[0, 2, 7]; [n le 3 select I[n] else 2*Self(n-1)-Self(n-2)+2*Self(n-3): n in [1..40]]; // Vincenzo Librandi, Jun 17 2012

LinearRecurrence[{2,-1,2},{0,2,7},40] (* Vincenzo Librandi, Jun 17 2012 *)

From R. J. Mathar, Feb 23 2008: (Start)
O.g.f.: -7/(5*(2x-1)) - (4x+7)/(5*(x^2+1)).
a(n) = (7*2^n - (-1)^floor(n/2)*A010712(n+1))/5. (End)
E.g.f.: (1/5)*(7*cosh(2*x) + 7*sinh(2*x) - 7*cos(x) - 4*sin(x)). - G. C. Greubel, Oct 18 2016

More terms from R. J. Mathar, Feb 23 2008

A182460 a(n) = (3/5)*2^(4n+1) - (1/5).

Original entry on oeis.org

1, 19, 307, 4915, 78643, 1258291, 20132659, 322122547, 5153960755, 82463372083, 1319413953331, 21110623253299, 337769972052787, 5404319552844595, 86469112845513523, 1383505805528216371, 22136092888451461939, 354177486215223391027, 5666839779443574256435, 90669436471097188102963, 1450710983537555009647411

Offset: 0

Brad Clardy, Apr 30 2012

Bisection of A112627.

Index entries for linear recurrences with constant coefficients, signature (17,-16).

Cf. A112627, A016029, A153893.

[(3/5)*2^(4*n+1) - (1/5): n in [0..20]];

(3*2^(4*Range[0,20]+1)-1)/5 (* or *) LinearRecurrence[{17,-16},{1,19},30] (* Harvey P. Dale, Jul 21 2021 *)

a(n) = (3/5)*2^(4*n+1) - (1/5).
a(n) = 16*a(n-1) + 3 for n > 0.
a(n) = (1/5)*A153893(4*n+1).
a(n) = A016029(4*n+2).
a(n) = A112627(2*n+1).
G.f.: (1+2*x)/((1-x)*(1-16*x)). - Colin Barker, May 06 2012

cp's OEIS Frontend

A113405 Expansion of x^3/(1 - 2x + x^3 - 2x^4) = x^3/( (1-2x)(1+x)*(1-x+x^2) ).

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A135541 a(n) = 2a(n-1) - a(n-2) + 2a(n-3), with a(0) = 2, a(1) = 2.

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A182460 a(n) = (3/5)*2^(4n+1) - (1/5).

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cp's OEIS Frontend

A113405 Expansion of x^3/(1 - 2*x + x^3 - 2*x^4) = x^3/( (1-2*x)*(1+x)*(1-x+x^2) ).

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A135541 a(n) = 2*a(n-1) - a(n-2) + 2*a(n-3), with a(0) = 2, a(1) = 2.

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A182460 a(n) = (3/5)*2^(4n+1) - (1/5).

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A113405 Expansion of x^3/(1 - 2x + x^3 - 2x^4) = x^3/( (1-2x)(1+x)*(1-x+x^2) ).

A135541 a(n) = 2a(n-1) - a(n-2) + 2a(n-3), with a(0) = 2, a(1) = 2.