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A134136 a(n) = 2*a(n-2) + 4*a(n-3), with initial terms 0, 1, 1. 2
0, 1, 1, 2, 6, 8, 20, 40, 72, 160, 304, 608, 1248, 2432, 4928, 9856, 19584, 39424, 78592, 157184, 314880, 628736, 1258496, 2516992, 5031936, 10067968, 20131840, 40263680, 80535552, 161054720, 322125824, 644251648, 1288470528, 2577006592, 5153947648, 10307895296 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

LINKS

Robert Israel, Table of n, a(n) for n = 0..2991

Index entries for linear recurrences with constant coefficients, signature (0,2,4).

FORMULA

a(n) = (6*2^n - (3+i)*(-1+i)^n - (3-i)*(-1-i)^n)/20. - Ivan Neretin, May 27 2015

G.f.: (x^2+x)/(1-2*x^2-4*x^3). - Robert Israel, May 27 2015

MAPLE

f:= gfun:-rectoproc({a(n)=2*a(n-2)+4*a(n-3), a(0)=0, a(1)=1, a(2)=1}, a(n), remember):

seq(f(n), n=0..100); # Robert Israel, May 27 2015

MATHEMATICA

Nest[Append[#, 2 #[[-2]] + 4 #[[-3]]] &, {0, 1, 1}, 15] (* Ivan Neretin, May 27 2015 *)

CoefficientList[Series[x (1 + x)/((1 - 2 x) (2 x^2 + 2 x + 1)), {x, 0, 40}], x] (* Vincenzo Librandi, May 28 2015 *)

PROG

(MAGMA) [n le 3 select Floor(n/2) else 2*Self(n-2)+4*Self(n-3): n in [1..40]]; // Vincenzo Librandi, May 28 2015

CROSSREFS

Cf. A134654.

Sequence in context: A064713 A162213 A100358 * A185165 A289892 A289095

Adjacent sequences:  A134133 A134134 A134135 * A134137 A134138 A134139

KEYWORD

nonn,easy

AUTHOR

Paul Curtz, Jan 29 2008

EXTENSIONS

More terms from Robert Israel, May 27 2015

STATUS

approved

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Last modified August 8 11:31 EDT 2020. Contains 336298 sequences. (Running on oeis4.)