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 A027474 a(n) = 7^(n-2) * C(n,2). 19
 1, 21, 294, 3430, 36015, 352947, 3294172, 29647548, 259416045, 2219448385, 18643366434, 154231485954, 1259557135291, 10173346092735, 81386768741880, 645668365352248, 5084638377148953, 39779817891812397, 309398583602985310 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,2 COMMENTS 7th binomial transform of (0,0,1,0,0,0,........). Starting at 1, the three-fold convolution of A000420 (powers of 7). - Paul Barry, Mar 08 2003 LINKS Vincenzo Librandi, Table of n, a(n) for n = 2..400 Index entries for linear recurrences with constant coefficients, signature (21,-147,343). FORMULA From Paul Barry, Mar 08 2003: (Start) G.f.: x^2 / (1-7*x)^3. a(n) = 21*a(n-1) - 147*a(n-2) + 343*a(n-3), a(0) = a(1) = 0, a(2) = 1. (End) Numerators of sequence a[3,n] in (a[i,j])^3 where a[i,j] = binomial(i-1, j-1)/2^(i-1) if j<=i, 0 if j>i. E.g.f.: (x^2/2)*exp(7*x). - G. C. Greubel, May 13 2021 From Amiram Eldar, Jan 06 2022: (Start) Sum_{n>=2} 1/a(n) = 14 - 84*log(7/6). Sum_{n>=2} (-1)^n/a(n) = 112*log(8/7) - 14. (End) MAPLE seq(binomial(n, 2)*7^(n-2), n=2..30); # Zerinvary Lajos, Jun 12 2008 MATHEMATICA Table[7^(n-2) Binomial[n, 2], {n, 2, 20}] (* Harvey P. Dale, Sep 25 2011 *) PROG (Sage) [7^(n-2)*binomial(n, 2) for n in range(2, 21)] # Zerinvary Lajos, Mar 13 2009 (MAGMA) [7^(n-2)* Binomial(n, 2): n in [2..20]]; /* Vincenzo Librandi, Oct 12 2011 */ (PARI) a(n)=7^(n-2)*n*(n-1)/2 \\ Charles R Greathouse IV, Oct 07 2015 CROSSREFS Third column of A027466. Sequences similar to the form q^(n-2)*binomial(n, 2): A000217 (q=1), A001788 (q=2), A027472 (q=3), A038845 (q=4), A081135 (q=5), A081136 (q=6), this sequence (q=7), A081138 (q=8), A081139 (q=9), A081140 (q=10), A081141 (q=11), A081142 (q=12), A027476 (q=15). Sequence in context: A025962 A181381 A081137 * A021864 A020570 A025940 Adjacent sequences:  A027471 A027472 A027473 * A027475 A027476 A027477 KEYWORD nonn,easy AUTHOR EXTENSIONS Edited by Ralf Stephan, Dec 30 2004 STATUS approved

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Last modified January 22 10:13 EST 2022. Contains 350481 sequences. (Running on oeis4.)