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 A116090 Expansion of 1/(1-x^2*(1+x)^3). 2
 1, 0, 1, 3, 4, 7, 16, 29, 52, 102, 194, 361, 685, 1301, 2452, 4633, 8771, 16577, 31327, 59241, 112004, 211724, 400285, 756786, 1430710, 2704817, 5113647, 9667590, 18277014, 34553692, 65325542, 123501151, 233485250, 441415867, 834519021 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,4 COMMENTS Diagonal sums of number triangle A116089. LINKS G. C. Greubel, Table of n, a(n) for n = 0..1000 Index entries for linear recurrences with constant coefficients, signature (0, 1, 3, 3, 1). FORMULA a(n) = a(n-2) + 3*a(n-3) + 3*a(n-4) + a(n-5). a(n) = Sum_{k=0..floor(n/2)} C(3*k, n-2*k). a(n) = Sum_{k=0..floor(n/2)} C(n-k,k)*C(4*k,n-k)/C(4*k,k). MATHEMATICA CoefficientList[Series[1/(1-x^2(1+x)^3), {x, 0, 40}], x] (* or *) LinearRecurrence[{0, 1, 3, 3, 1}, {1, 0, 1, 3, 4}, 40] (* Harvey P. Dale, Apr 28 2014 *) PROG (PARI) {a(n) = sum(k=0, floor(n/2), binomial(3*k, n-2*k))}; \\ G. C. Greubel, May 09 2019 (MAGMA) [(&+[Binomial(3*k, n-2*k): k in [0..Floor(n/2)]]): n in [0..40]]; // G. C. Greubel, May 09 2019 (Sage) [sum(binomial(3*k, n-2*k) for k in (0..floor(n/2))) for n in (0..40)] # G. C. Greubel, May 09 2019 CROSSREFS Sequence in context: A027020 A130755 A286348 * A287741 A291710 A100455 Adjacent sequences:  A116087 A116088 A116089 * A116091 A116092 A116093 KEYWORD easy,nonn AUTHOR Paul Barry, Feb 04 2006 STATUS approved

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Last modified January 17 18:14 EST 2020. Contains 330987 sequences. (Running on oeis4.)