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A015521 a(n) = 3*a(n-1) + 4*a(n-2), a(0) = 0, a(1) = 1. 48
0, 1, 3, 13, 51, 205, 819, 3277, 13107, 52429, 209715, 838861, 3355443, 13421773, 53687091, 214748365, 858993459, 3435973837, 13743895347, 54975581389, 219902325555, 879609302221, 3518437208883, 14073748835533 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

Inverse binomial transform of powers of 5 (A000351) preceded by 0. - Paul Barry, Apr 02 2003

Number of walks of length n between any two distinct vertices of the complete graph K_5. Example: a(2)=3 because the walks of length 2 between the vertices A and B of the complete graph ABCDE are: ACB, ADB, AEB. - Emeric Deutsch, Apr 01 2004

The terms of the sequence are the number of segments (sides) per iteration of the space-filling Peano-Hilbert curve. - Giorgio Balzarotti, Mar 16 2006

General form: k=4^n-k. Also: A001045, A078008, A097073, A115341, A015518, A054878. - Vladimir Joseph Stephan Orlovsky, Dec 11 2008

A further inverse binomial transform generates A015441. - Paul Curtz, Nov 01 2009

For n>=2, a(n) equals the permanent of the (n-1) X (n-1) tridiagonal matrix with 3's along the central diagonal, and 2's along the subdiagonal and the superdiagonal. - John M. Campbell, Jul 19 2011

Pisano period lengths: 1, 1, 2, 2, 10, 2, 6, 2, 6, 10, 10, 2, 6, 6, 10, 2, 4, 6, 18, 10, ... - R. J. Mathar, Aug 10 2012

Sum( (-1)^(m+i)*4^i, i=0..m ), for m>=0, gives the terms after 0. - Bruno Berselli, Aug 28 2013

The ratio a(n+1)/a(n) converges to 4 as n approaches infinity. - Felix P. Muga II, Mar 09 2014

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..1000

Index entries for sequences related to linear recurrences with constant coefficients, signature (3,4).

FORMULA

a(n) = 4^n/5-(-1)^n/5. E.g.f.: (exp(4*x)-exp(-x))/5. - Paul Barry, Apr 02 2003

a(n) = sum{k=1..n, binomial(n, k)(-1)^(n+k)*5^(k-1) }. - Paul Barry, May 13 2003

a(2*n) = 4*a(2*n-1) -1, a(2*n+1) = 4*a(2*n) +1. In general this is true for all sequences of the type a(n) +a(n+1) = q^(n): i.e., a(2*n) = q*a(2n-1) - 1 and a(2*n+1) = q*a(2*n) + 1. - Amarnath Murthy, Jul 15 2003

a(n) = 4^(n-1) - a(n-1). G.f.: x/(1-3*x-4*x^2). - Emeric Deutsch, Apr 01 2004

a(n+1) = sum{k=0..floor(n/2), binomial(n-k, k)*3^(n-2k)*4^k}. - Paul Barry, Jul 29 2004

a(n) = 4*a(n-1)-(-1)^n, n>0, a(0)=0. - Paul Barry, Aug 25 2004

a(n) = Sum_{k, 0<=k<=n} A155161(n,k)*2^(n-k), n>=1. - Philippe Deléham, Jan 27 2009

a(n) = round(4^n/5). - Mircea Merca, Dec 28 2010

The logarithmic generating function 1/5*log((1+x)/(1-4*x)) = x + 3*x^2/2 + 13*x^3/3 + 51*x^4/4 + ... has compositional inverse 5/(4+exp(-5*x)) - 1, the e.g.f. for a signed version of A213127. - Peter Bala, Jun 24 2012

a(n)=(-1)^(n-1)*sum(k=0,..,n-1, A135278(n-1,k)*(-5)^k) = [4^n-(-1)^n]/5 = (-1)^(n-1)*sum(k=0,..,n-1, (-4)^k). Equals (-1)^(n-1)*Phi(n,-4), where Phi is the cyclotomic polynomial when n is an odd prime. (For n>0.) - Tom Copeland, Apr 14 2014

EXAMPLE

G.f. = x + 3*x^2 + 13*x^3 + 51*x^4 + 205*x^5 + 819*x^6 + 3277*x^7 + 13107*x^8 + ...

MAPLE

seq(round(4^n/5), n=0..25) # Mircea Merca, Dec 28 2010

MATHEMATICA

k=0; lst={k}; Do[k=4^n-k; AppendTo[lst, k], {n, 0, 5!}]; lst (* Vladimir Joseph Stephan Orlovsky, Dec 11 2008 *)

LinearRecurrence[{3, 4}, {0, 1}, 30] (* Harvey P. Dale, Jun 26 2012 *)

CoefficientList[Series[x/((1 - 4 x) (1 + x)), {x, 0, 50}], x] (* Vincenzo Librandi, Mar 26 2014 *)

PROG

(Sage) [lucas_number1(n, 3, -4) for n in xrange(0, 24)] # Zerinvary Lajos, Apr 22 2009

(MAGMA) [Floor(4^n/5-(-1)^n/5): n in [0..30]]; // Vincenzo Librandi, Jun 24 2011

CROSSREFS

Cf. A001045, A078008, A097073, A115341, A015518, A054878, A201455, A213127.

Sequence in context: A244784 A197074 A014985 * A146279 A098619 A086608

Adjacent sequences:  A015518 A015519 A015520 * A015522 A015523 A015524

KEYWORD

nonn,easy

AUTHOR

Olivier Gérard

STATUS

approved

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Last modified December 18 15:01 EST 2014. Contains 252161 sequences.