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 A003053 Order of orthogonal group O(n, GF(2)). (Formerly M1716) 5
 1, 2, 6, 48, 720, 23040, 1451520, 185794560, 47377612800, 24257337753600, 24815256521932800, 50821645356918374400, 208114637736580743168000, 1704875112338069448032256000, 27930968965434591767112450048000, 915241991059360703024740763172864000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 REFERENCES N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS T. D. Noe, Table of n, a(n) for n = 1..41 J. H. Conway et al., ATLAS of Finite Groups, Chapter 2. F. J. MacWilliams, Orthogonal matrices over finite fields, Amer. Math. Monthly, 76 (1969), 152-164. FORMULA For formulas see Maple code. Asymptotics: a(n) ~ c * 2^((n^2-n)/2), where c = (1/4; 1/4)_infinity ~ 0.6885375... is expressed in terms of the Q-Pochhammer symbol. - Cedric Lorand, Aug 07 2017 MAPLE h:=proc(n) local m; if n mod 2 = 0 then m:=n/2; 2^(m^2)*mul( 4^i-1, i=1..m); else m:=(n+1)/2; 2^(m^2)*mul( 4^i-1, i=1..m-1); fi; end; # This produces a(n+1) PROG (PARI) a(n) = n--; if (n % 2, m = (n+1)/2; 2^(m^2)*prod(k=1, m-1, 4^k-1), m = n/2; 2^(m^2)*prod(k=1, m, 4^k-1)); \\ Michel Marcus, Jul 13 2017 (Python) def size_binary_orthogonal_group(n): ....k = n-1 ....if k%2==0: ......m=k//2 ......p=2**(m**2) ......for i in range(1, m+1): ........p*=4**i-1 ....else: ........m=(k+1)//2 ........p=2**(m**2) ........for i in range(1, m): ............p*=4**i-1 ....return p #call and print output for a(n) print([size_binary_orthogonal_group(n) for n in range(1, 10)]) # Nathan J. Russell, Nov 01 2017 CROSSREFS Bisections give A003923 and A090770. Sequence in context: A052717 A175430 A129464 * A113296 A275462 A063744 Adjacent sequences:  A003050 A003051 A003052 * A003054 A003055 A003056 KEYWORD nonn,easy AUTHOR EXTENSIONS Edited by N. J. A. Sloane, Dec 30 2008 Edited by W. Edwin Clark et al., Jan 15 2015 STATUS approved

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Last modified October 14 03:00 EDT 2019. Contains 327995 sequences. (Running on oeis4.)