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 A054147 a(n) = T(2n,n), array T as in A054144. 1
 0, 3, 21, 108, 492, 2100, 8604, 34272, 133728, 513648, 1948560, 7318080, 27256896, 100815936, 370684608, 1355996160, 4938304512, 17914202880, 64760732928, 233390693376, 838784916480, 3006980379648, 10755352869888 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 LINKS G. C. Greubel, Table of n, a(n) for n = 0..1000 Index entries for linear recurrences with constant coefficients, signature (8,-20,16,-4). FORMULA G.f.: 3*x*(1-x)/(1-4*x+2*x^2)^2. From Colin Barker, Aug 01 2019: (Start) a(n) = 8*a(n-1) - 20*a(n-2) + 16*a(n-3) - 4*a(n-4) for n>3. a(n) = 3*((-(2-sqrt(2))^n*(-1+sqrt(2)) + (1+sqrt(2))*(2+sqrt(2))^n)*n) / 8. (End) MATHEMATICA LinearRecurrence[{8, -20, 16, -4}, {0, 3, 21, 108}, 30] (* G. C. Greubel, Jul 31 2019 *) PROG (PARI) my(x='x+O('x^30)); concat([0], Vec(3*x*(1-x)/(1-4*x+2*x^2)^2)) \\ G. C. Greubel, Jul 31 2019 (MAGMA) R:=PowerSeriesRing(Integers(), 30); [0] cat Coefficients(R!( 3*x*(1-x)/(1-4*x+2*x^2)^2 )); // G. C. Greubel, Jul 31 2019 (Sage) (3*x*(1-x)/(1-4*x+2*x^2)^2).series(x, 30).coefficients(x, sparse=False) # G. C. Greubel, Jul 31 2019 (GAP) a:=[0, 3, 21, 108];; for n in [5..30] do a[n]:=8*a[n-1]-20*a[n-2] +16*a[n-3]-4*a[n-4]; od; a; # G. C. Greubel, Jul 31 2019 CROSSREFS Cf. A054144. Sequence in context: A128281 A034268 A140451 * A233582 A043012 A122120 Adjacent sequences:  A054144 A054145 A054146 * A054148 A054149 A054150 KEYWORD nonn,easy AUTHOR Clark Kimberling, Mar 18 2000 STATUS approved

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Last modified December 13 23:14 EST 2019. Contains 329974 sequences. (Running on oeis4.)