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A002820 Number of n X n invertible binary matrices A such that A+I is invertible.
(Formerly M2170 N0866)

%I M2170 N0866

%S 0,2,48,5824,2887680,5821595648,47317927329792,1544457148312846336,

%T 202039706313624586813440,105823549214125066767168438272,

%U 221819704567105547916502447159246848

%N Number of n X n invertible binary matrices A such that A+I is invertible.

%C Also number of linear orthomorphisms of GF(2)^n.

%D N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).

%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

%H Vincenzo Librandi, <a href="/A002820/b002820.txt">Table of n, a(n) for n = 1..55</a>

%H Zong Duo Dai, Solomon W. Golomb, Guang Gong, <a href="http://dx.doi.org/10.1016/S0012-365X(99)00035-7">Generating all linear orthomorphisms without repetition</a>, Discrete Math. 205 (1999), 47-55.

%H P. F. Duvall, Jr. and P. W. Harley, III, <a href="http://www.jstor.org/stable/2099958">A note on counting matrices</a>, SIAM J. Appl. Math., 20 (1971), 374-377.

%H Kent Morrison, <a href="http://www.calpoly.edu/~kmorriso/Research/mnev01.pdf">Matrices over F_q with no eigenvalues of 0 or 1</a>

%H Kent E. Morrison, <a href="http://www.cs.uwaterloo.ca/journals/JIS/VOL9/Morrison/morrison37.html">Integer Sequences and Matrices Over Finite Fields</a>, Journal of Integer Sequences, Vol. 9 (2006), Article 06.2.1.

%H <a href="/index/Mat#binmat">Index entries for sequences related to binary matrices</a>

%F Reference gives a recurrence.

%F a(n) = 2^(n(n-1)/2) * A005327(n+1).

%p (Maple program based on Dai et al. from _N. J. A. Sloane_, Aug 10 2011)

%p N:=proc(n,i) option remember; if i = 1 then 1 else (2^n-2^(i-1))*N(n,i-1); fi; end;

%p Oh:=proc(n) option remember; local r; global N;

%p if n=0 then RETURN(1) elif n=1 then RETURN(0) else

%p add( 2^(r-2)*N(n,r)*2^(r*(n-r))*Oh(n-r), r=2..n); fi; end;

%p [seq(Oh(n),n=1..15)];

%t ni[n_, i_] := ni[n, i] = If[i == 1, 1, (2^n - 2^(i-1))*ni[n, i-1]]; a[0] = 1; a[1] = 0; a[n_] := a[n] = Sum[ 2^(r-2)*ni[n, r]*2^(r*(n-r))*a[n-r], {r, 2, n}]; Table[a[n], {n, 1, 11}] (* _Jean-Fran├žois Alcover_, Jan 19 2012, after Maple *)

%Y Cf. A002884.

%K nonn,nice,easy

%O 1,2

%A _N. J. A. Sloane_.

%E More terms from _Vladeta Jovovic_, Mar 17 2000

%E Entry revised by _N. J. A. Sloane_, Aug 10 2011

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Last modified August 10 06:23 EDT 2020. Contains 336368 sequences. (Running on oeis4.)