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A219977
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Expansion of 1/(1+x+x^2+x^3).
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7
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1, -1, 0, 0, 1, -1, 0, 0, 1, -1, 0, 0, 1, -1, 0, 0, 1, -1, 0, 0, 1, -1, 0, 0, 1, -1, 0, 0, 1, -1, 0, 0, 1, -1, 0, 0, 1, -1, 0, 0, 1, -1, 0, 0, 1, -1, 0, 0, 1, -1, 0, 0, 1, -1, 0, 0, 1, -1, 0, 0, 1, -1, 0, 0, 1, -1, 0, 0, 1, -1, 0, 0, 1, -1, 0, 0, 1, -1, 0, 0
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OFFSET
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0,1
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LINKS
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Elena Barcucci, Antonio Bernini, Stefano Bilotta, Renzo Pinzani, Non-overlapping matrices, arXiv:1601.07723 [cs.DM], 2016.
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FORMULA
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G.f.: 1/(1 +x +x^2 +x^3).
Euler transform of length 4 sequence [ -1, 0, 0, 1]. - Michael Somos, Dec 12 2012
A038505(n+2) = p(-1) where p(x) is the unique degree-n polynomial such that p(k) = a(k) for k = 0, 1, ..., n. - Michael Somos, Dec 12 2012
a(n) +a(n-1) +a(n-2) +a(n-3) = 0.
a(n) = (-1)^n/2 +(-1)^(n/2 +1/4 -(-1)^n/4)/2. (End)
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EXAMPLE
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G.f. = 1 - x + x^4 - x^5 + x^8 - x^9 + x^12 - x^13 + x^16 - x^17 + x^20 - x^21 + ...
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MATHEMATICA
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CoefficientList[Series[1/(1+x+x^2+x^3), {x, 0, 80}], x] (* or *) PadRight[{}, 120, {1, -1, 0, 0}]
LinearRecurrence[{-1, -1, -1}, {1, -1, 0}, 80] (* Harvey P. Dale, May 22 2021 *)
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PROG
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(PARI) {a(n) = [1, -1, 0, 0][n%4 + 1]} /* Michael Somos, Dec 12 2012 */
(PARI) Vec(1/(1+x+x^2+x^3) + O(x^100)) \\ Michel Marcus, Jan 28 2016
(Magma) m:=100; R<x>:=PowerSeriesRing(Integers(), m); Coefficients(R!(1/(1+x+x^2+x^3))); // Vincenzo Librandi, Apr 22 2015
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CROSSREFS
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KEYWORD
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sign,easy
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AUTHOR
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STATUS
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approved
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