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 A098589 a(n) = 3*a(n-1) + 2*a(n-3), with a(0)=1, a(1)=3. 1
 1, 3, 9, 29, 93, 297, 949, 3033, 9693, 30977, 98997, 316377, 1011085, 3231249, 10326501, 33001673, 105467517, 337055553, 1077170005, 3442445049, 11001446253, 35158678769, 112360926405, 359085671721, 1147574372701 (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 (3,0,2). FORMULA G.f.: 1/(1-3*x-2*x^3). a(n) = Sum_{k=0..floor(n/2)} Sum_{i=0..n} Sum_{j=0..i} C(n-2*k,i)*C(i,j) *C(j, k)*2^k. MATHEMATICA CoefficientList[Series[1/(1-3*x-2*x^3), {x, 0, 50}], x] (* or *) LinearRecurrence[{3, 0, 2}, {1, 3, 9}, 50] (* G. C. Greubel, Feb 03 2018 *) PROG (PARI) x='x+O('x^30); Vec(1/(1-3*x-2*x^3)) \\ G. C. Greubel, Feb 03 2018 (MAGMA) I:=[1, 3, 9]; [n le 3 select I[n] else 3*Self(n-1) + 2*Self(n-3): n in [1..30]]; // G. C. Greubel, Feb 03 2018 CROSSREFS Cf. A052541. Sequence in context: A303546 A135142 A195624 * A024744 A024964 A061534 Adjacent sequences:  A098586 A098587 A098588 * A098590 A098591 A098592 KEYWORD easy,nonn AUTHOR Paul Barry, Sep 16 2004 STATUS approved

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Last modified August 6 19:52 EDT 2020. Contains 336256 sequences. (Running on oeis4.)