(MAGMAMagma) I:=[1, 21, 292, 3402]; [n le 4 select I[n] else 21*Self(n-1)-149*Self(n-2)+399*Self(n-3)-270*Self(n-4): n in [1..25]]; /* or */ m:=25; R<x>:=PowerSeriesRing(Integers(), m); Coefficients(R!(1/((1-x)*(1-5*x)*(1-6*x)*(1-9*x)))); // Vincenzo Librandi, Jul 12 2013
<a href="/index/Rec">Index to sequences with entries for linear recurrences with constant coefficients</a>, signature (21,-149,399,-270).
<a href="/index/Rea#recLCCRec">Index to sequences with linear recurrences with constant coefficients</a>, signature (21,-149,399,-270).
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(PARI) a(n) = (5*9^(n+3) - 32*6^(n+3) + 30*5^(n+3) - 3)/480; \\ Joerg Arndt, Aug 13 2013
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a(n) = (5*9^(n+3) - 32*6^(n+3) + 30*5^(n+3) - 3)/480. [Yahia Kahloune, Aug 13 2013]
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CoefficientList[Series[1 / ((1 - x) (1 - 5 x) (1 - 6 x) (1 - 9 x)), {x, 0, 20}], x] (* Vincenzo Librandi, Jul 12 2013 *)
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