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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
OFFSET
0,4
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
KEYWORD
nonn,easy
AUTHOR
Paul Curtz, Jan 29 2008
EXTENSIONS
More terms from Robert Israel, May 27 2015
STATUS
approved