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 A049606 Largest odd divisor of n!, 26
 1, 1, 1, 3, 3, 15, 45, 315, 315, 2835, 14175, 155925, 467775, 6081075, 42567525, 638512875, 638512875, 10854718875, 97692469875, 1856156927625, 9280784638125, 194896477400625, 2143861251406875, 49308808782358125, 147926426347074375, 3698160658676859375 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,4 COMMENTS Original name: Denominator of 2^n/n!. a(n) = A000265(A000142(n)). - Reinhard Zumkeller, Apr 09 2004 For positive n, a(n) equals the numerator of the permanent of the n X n matrix whose (i,j)-entry is cos(i*Pi/3)*cos(j*Pi/3) (see example below). - John M. Campbell, May 28 2011 LINKS T. D. Noe, Table of n, a(n) for n = 0..100 FORMULA a(n) = Product_{k=1..n} A000265(k). a(n) = numerator(2*sum_{i=1..infinity} (-1)^i*(1-zeta(n+i+1)) * (product_{j=1..n} i+j)). - Gerry Martens, Mar 10 2011 a(n) = denominator([t^n] 1/(tanh(t)-1)). - Peter Luschny, Aug 04 2011 a(n) = n!/2^A011371(n). - Robert Israel, Jul 23 2015 EXAMPLE The numerator of the permanent of the following 5 X 5 matrix is equal to a(5): |  1/4  -1/4  -1/2  -1/4   1/4 | | -1/4   1/4   1/2   1/4  -1/4 | | -1/2   1/2    1    1/2  -1/2 | | -1/4   1/4   1/2   1/4  -1/4 | |  1/4  -1/4  -1/2  -1/4   1/4 | - John M. Campbell, May 28 2011 MAPLE f:= n-> n! * 2^(add(i, i=convert(n, base, 2))-n); # Peter Luschny, May 02 2009 seq (denom (coeff (series(1/(tanh(t)-1), t, 30), t, n)), n=0..25); # Peter Luschny, Aug 04 2011 seq(numer(n!/2^n), n=0..100); # Robert Israel, Jul 23 2015 MATHEMATICA Denominator[Table[(2^n)/n!, {n, 0, 40}]] (* Vladimir Joseph Stephan Orlovsky, Apr 03 2011*) Table[Last[Select[Divisors[n!], OddQ]], {n, 0, 30}] (* Harvey P. Dale, Jul 24 2016 *) Table[n!/2^IntegerExponent[n!, 2], {n, 1, 30}] (* Clark Kimberling, Oct 22 2016 *) PROG (MAGMA) [ Denominator(2^n/Factorial(n)): n in [0..25] ]; // Klaus Brockhaus, Mar 10 2011 (PARI) A049606(n)=local(f=n!); f/2^valuation(f, 2); \\ Joerg Arndt, Apr 22 2011 CROSSREFS Numerators give A001316. Cf. A000680, A008977, A139541. Factor of A160481. - Johannes W. Meijer, May 24 2009 Equals A003148 divided by A123746. - Johannes W. Meijer, Nov 23 2009 Different from A160624. Cf. A011371. Sequence in context: A067655 A209430 A160624 * A046126 A143257 A089403 Adjacent sequences:  A049603 A049604 A049605 * A049607 A049608 A049609 KEYWORD nonn,frac,easy AUTHOR N. J. A. Sloane, Feb 05 2000 EXTENSIONS New name (from Amarnath Murthy) by Charles R Greathouse IV, Jul 23 2015 STATUS approved

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Last modified December 14 09:20 EST 2018. Contains 318091 sequences. (Running on oeis4.)