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 A138897 Ratio of (2n-1)! to number of zeros in upper part of Sylvester matrix of polynomial of degree n with all nonzero coefficients. 1
 3, 20, 420, 18144, 1330560, 148262400, 23351328000, 4940103168000, 1351612226764800, 464463110651904000, 195848611658219520000, 99430833611096064000000, 59828953024276660224000000, 42103628541617628354969600000, 34261827725741345073856512000000, 31923961833867229762934538240000000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,1 COMMENTS From Anthony Hernandez, Oct 24 2017: (Start) If (n,n-1) is the two-part partition of any odd integer greater than 1 then a(n-1) is the number of permutations of shape (n,n-1). For example, the two-part partition of 11 with shape (n,n-1) is (6,5). Pictorially we can draw this as a standard Young diagram with cells populated by hook lengths:           (6,5) = 7 6 5 4 3 1                   5 4 3 2 1   and there are a(6-1) = a(5) = 1330560 permutations with shape (6,5). (End) LINKS FORMULA a(n) = (2n - 1)!/(n*(n - 1)) for n >= 2. MAPLE A138897:=n->(2*n - 1)!/(n*(n - 1)): seq(A138897(n), n=2..20); # Wesley Ivan Hurt, Nov 25 2017 MATHEMATICA Table[(2 n - 1)!/(n (n - 1)), {n, 2, 20}] PROG (PARI) a(n) = (2*n - 1)!/(n*(n - 1)); \\ Michel Marcus, Oct 28 2017 CROSSREFS Cf. A002378, A009445, A007878, A138896, A138898, A000108. Sequence in context: A326869 A203194 A322455 * A189603 A203228 A174972 Adjacent sequences:  A138894 A138895 A138896 * A138898 A138899 A138900 KEYWORD nonn AUTHOR Artur Jasinski, Apr 02 2008 EXTENSIONS More terms from Michel Marcus, Oct 28 2017 STATUS approved

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Last modified January 20 19:53 EST 2022. Contains 350472 sequences. (Running on oeis4.)