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 A027790 a(n) = 10*(n+1)*binomial(n+3,5)/3. 1
 10, 80, 350, 1120, 2940, 6720, 13860, 26400, 47190, 80080, 130130, 203840, 309400, 456960, 658920, 930240, 1288770, 1755600, 2355430, 3116960, 4073300, 5262400, 6727500, 8517600, 10687950, 13300560, 16424730, 20137600 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,1 LINKS Index entries for linear recurrences with constant coefficients, signature (7, -21, 35, -35, 21, -7, 1). FORMULA Number of 9-subsequences of [ 1, n ] with just 3 contiguous pairs. G.f.: 10*(1+x)*x^2/(1-x)^7. a(n) = binomial(n+1, 3)*binomial(n+3, 3) = A000292(n-1)*A000292(n+1). - Zerinvary Lajos, May 13 2005 a(n) = 10*A040977(n). - R. J. Mathar, May 22 2013 MATHEMATICA Table[10(n+1) Binomial[n+3, 5]/3, {n, 2, 30}] (* or *) LinearRecurrence[{7, -21, 35, -35, 21, -7, 1}, {10, 80, 350, 1120, 2940, 6720, 13860}, 30] (* Harvey P. Dale, Jan 15 2015 *) CROSSREFS Sequence in context: A206764 A253649 A244729 * A000575 A220485 A055285 Adjacent sequences:  A027787 A027788 A027789 * A027791 A027792 A027793 KEYWORD nonn,easy AUTHOR thi ngoc dinh (via R. K. Guy) STATUS approved

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Last modified February 28 08:28 EST 2020. Contains 332323 sequences. (Running on oeis4.)