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A224749
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Vauban's sequence: a(n)=0 if n<=0, a(1)=1; thereafter a(n) = 3*a(n-1) + 6*a(n-2) + 6*a(n-3) + 6*a(n-4) + 6*a(n-5).
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1
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0, 1, 3, 15, 69, 321, 1491, 6921, 32139, 149229, 692919, 3217437, 14939559, 69369021, 322101927, 1495619397, 6944625855, 32246056989, 149728468167, 695235829509, 3228196110975, 14989518216045, 69600993441975, 323179052074101, 1500620817813327, 6967849012498557, 32353889326768359
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OFFSET
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0,3
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COMMENTS
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In his essay "La Cochonnerie ou calcul estimatif...", French military engineer Vauban (1633-1707) writes about this Fibonacci-like sequence for the year-by-year growth of pigs. - Charles R Greathouse IV, Sep 16 2015
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REFERENCES
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Sébastien Le Prestre de Vauban, La cochonnerie ou calcul estimatif pour connaître jusqu'où peut aller la production d'une truie pendant dix années de temps (1699).
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LINKS
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FORMULA
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MAPLE
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f:=proc(n) option remember;
if n <= 0 then 0 elif n=1 then 1 else
3*f(n-1)+6*f(n-2)+6*f(n-3)+6*f(n-4)+6*f(n-5); fi; end;
[seq(f(n), n=0..30)];
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MATHEMATICA
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LinearRecurrence[{3, 6, 6, 6, 6}, {0, 1, 3, 15, 69}, 40] (* T. D. Noe, Apr 17 2013 *)
CoefficientList[Series[x/(1 - 3 x - 6 x^2 - 6 x^3 - 6 x^4 - 6 x^5), {x, 0, 33}], x] (* Vincenzo Librandi, Sep 17 2015 *)
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PROG
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(PARI) a(n)=([0, 1, 0, 0, 0; 0, 0, 1, 0, 0; 0, 0, 0, 1, 0; 0, 0, 0, 0, 1; 6, 6, 6, 6, 3]^n*[0; 1; 3; 15; 69])[1, 1] \\ Charles R Greathouse IV, Sep 16 2015
(Magma) I:=[0, 1, 3, 15, 69]; [n le 5 select I[n] else 3*Self(n-1)+6*Self(n-2)+6*Self(n-3)+6*Self(n-4)+6*Self(n-5): n in [1..30]]; // Vincenzo Librandi, Sep 17 2015
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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Pierre de la Harpe, Apr 17 2013
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STATUS
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approved
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