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A077856
Expansion of (1-x)^(-1)/(1-2*x+x^2+x^3).
2
1, 3, 6, 9, 10, 6, -6, -27, -53, -72, -63, 0, 136, 336, 537, 603, 334, -471, -1878, -3618, -4886, -4275, -45, 9072, 22465, 35904, 40272, 22176, -31823, -126093, -242538, -327159, -285686, -1674, 609498, 1506357, 2404891, 2693928, 1476609, -2145600, -8461736, -16254480, -21901623
OFFSET
0,2
FORMULA
a(n) = Sum_{k=1..floor(n/3+1)} (-1)^k*binomial(n-k+3, 2*k). - Vladeta Jovovic, Feb 10 2003
a(n) = 3*a(n-1) - 3*a(n-2) + a(n-4). - Chai Wah Wu, May 25 2016
MATHEMATICA
LinearRecurrence[{3, -3, 0, 1}, {1, 3, 6, 9}, 50] (* Vincenzo Librandi, May 27 2016 *)
PROG
(PARI) Vec((1-x)^(-1)/(1-2*x+x^2+x^3)+O(x^99)) \\ Charles R Greathouse IV, Sep 27 2012
(Magma) I:=[1, 3, 6, 9]; [n le 4 select I[n] else 3*Self(n-1)-3*Self(n-2)+Self(n-4): n in [1..50]]; // Vincenzo Librandi, May 27 2016
CROSSREFS
Cf. A078001.
Sequence in context: A159785 A057338 A337603 * A239977 A074499 A309584
KEYWORD
sign,easy
AUTHOR
N. J. A. Sloane, Nov 17 2002
STATUS
approved