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 A027476 Third column of A027467. 13
 1, 45, 1350, 33750, 759375, 15946875, 318937500, 6150937500, 115330078125, 2114384765625, 38058925781250, 674680957031250, 11806916748046875, 204350482177734375, 3503151123046875000, 59553569091796875000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 3,2 LINKS Vincenzo Librandi, Table of n, a(n) for n = 3..200 Index entries for linear recurrences with constant coefficients, signature (45,-675,3375). FORMULA Numerators of sequence a[3,n] in (a[i,j])^4 where a[i,j] = binomial(i-1, j-1)/2^(i-1) if j<=i, 0 if j>i. a(n) = 15^(n-3)*binomial(n-1, 2). From G. C. Greubel, May 13 2021: (Start) a(n) = 45*a(n-1) - 675*a(n-2) + 3375*a(n-3). G.f.: x^3/(1 - 15*x)^3. E.g.f.: (-2 + (2 - 30*x + 225*x^2)*exp(15*x))/6750. (End) From Amiram Eldar, Jan 06 2022: (Start) Sum_{n>=3} 1/a(n) = 30 - 420*log(15/14). Sum_{n>=3} (-1)^(n+1)/a(n) = 480*log(16/15) - 30. (End) MAPLE seq((15)^(n-3)*binomial(n-1, 2), n=3..30) # G. C. Greubel, May 13 2021 MATHEMATICA Table[(n-1)*(n-2)/2 * 15^(n-3), {n, 3, 30}] (* Vincenzo Librandi, Dec 29 2012 *) PROG (MAGMA) [(n-1)*(n-2)/2 * 15^(n-3): n in [3..20]]; // Vincenzo Librandi, Dec 29 2012 (Sage) [(15)^(n-3)*binomial(n-1, 2) for n in (3..30)] # G. C. Greubel, May 13 2021 CROSSREFS 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), A027474 (q=7), A081138 (q=8), A081139 (q=9), A081140 (q=10), A081141 (q=11), A081142 (q=12), this sequence (q=15). Sequence in context: A346324 A243570 A145151 * A062262 A137716 A035521 Adjacent sequences:  A027473 A027474 A027475 * A027477 A027478 A027479 KEYWORD nonn AUTHOR STATUS approved

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Last modified January 23 11:16 EST 2022. Contains 350512 sequences. (Running on oeis4.)