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 A027820 a(n) = 28*(n+1)*C(n+6,8)/3. 0
 28, 336, 2100, 9240, 32340, 96096, 252252, 600600, 1321320, 2722720, 5309304, 9876048, 17635800, 30387840, 50736840, 82372752, 130423524, 201894000, 306205900, 455855400, 667206540, 961440480, 1365682500 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,1 LINKS Index entries for linear recurrences with constant coefficients, signature (10,-45,120,-210,252,-210,120,-45,10,-1). FORMULA Number of 15-subsequences of [ 1, n ] with just 6 contiguous pairs; g.f. 28*(1+2x)*x^2/(1-x)^10. a(n) = C(n+1, 3)*C(n+6, 6). - Zerinvary Lajos, Jun 08 2005, corrected by R. J. Mathar, Feb 10 2016 MATHEMATICA Table[28(n+1) Binomial[n+6, 8]/3, {n, 2, 30}] (* or *) LinearRecurrence[{10, -45, 120, -210, 252, -210, 120, -45, 10, -1}, {28, 336, 2100, 9240, 32340, 96096, 252252, 600600, 1321320, 2722720}, 30] PROG (PARI) a(n)=28*(n+1)*binomial(n+6, 8)/3 \\ Charles R Greathouse IV, May 22 2013 CROSSREFS Sequence in context: A241038 A055753 A159520 * A092713 A134288 A200968 Adjacent sequences:  A027817 A027818 A027819 * A027821 A027822 A027823 KEYWORD nonn,easy AUTHOR thi ngoc dinh (via R. K. Guy) STATUS approved

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Last modified April 4 05:31 EDT 2020. Contains 333212 sequences. (Running on oeis4.)