OFFSET
0,2
COMMENTS
For n >= 1, a(n) is the number of n X n (0, 1) matrices.
Also number of directed graphs on n labeled nodes allowing self-loops (cf. A053763).
1/2^(n^2) is the Hankel transform of C(n, n/2)*(1 + (-1)^n)/(2*2^n), or C(2n, n)/4^n with interpolated zeros. - Paul Barry, Sep 27 2007
Hankel transform of A064062. - Philippe Deléham, Nov 19 2007
a(n) is also the order of the semigroup (monoid) of all binary relations on an n-set. - Abdullahi Umar, Sep 14 2008
With offset = 1, a(n) is the number of n X n (0, 1) matrices with an even number of 1's in every row and in every column. - Geoffrey Critzer, May 23 2013
a(n) is the number of functions from an n-set to its power set (by definition of function including the empty function only when n = 0). - Rick L. Shepherd, Dec 27 2014
REFERENCES
John M. Howie, Fundamentals of semigroup theory. Oxford: Clarendon Press, (1995). - Abdullahi Umar, Sep 14 2008
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..33
Peter J. Cameron, Sequences realized by oligomorphic permutation groups, J. Integ. Seqs. Vol. 3 (2000), #00.1.5.
Theresia Eisenkölbl, 2-Enumerations of halved alternating sign matrices, arXiv:math/0106038 [math.CO], 2001.
Theresia Eisenkölbl, 2-Enumerations of halved alternating sign matrices, Séminaire Lotharingien Combin. 46, (2001), Article B46c, 11 pp.
Daniele A. Gewurz and Francesca Merola, Sequences realized as Parker vectors of oligomorphic permutation groups, J. Integer Seqs., Vol. 6, 2003.
F. Harary and R. W. Robinson, Labeled bipartite blocks, Canad. J. Math., 31 (1979), 60-68.
S. R. Kannan and Rajesh Kumar Mohapatra, Counting the Number of Non-Equivalent Classes of Fuzzy Matrices Using Combinatorial Techniques, arXiv:1909.13678 [math.GM], 2019.
Kent E. Morrison, Integer Sequences and Matrices Over Finite Fields, Journal of Integer Sequences, Vol. 9 (2006), Article 06.2.1.
Götz Pfeiffer, Counting Transitive Relations, Journal of Integer Sequences, Vol. 7 (2004), Article 04.3.2.
Eric Weisstein's World of Mathematics, 01-Matrix.
FORMULA
G.f. satisfies: A(x) = 1 + 2*x*A(4x). - Paul D. Hanna, Dec 04 2009
a(n) = 2^n * Sum_{i = 0..C(n, 2)} C(C(n, 2), i)*3^i. The summation conditions on the number of symmetric pairs (a,b) with a<b in an n X n binary matrix. Cf. A027465, A013610. - Geoffrey Critzer, Nov 05 2024
G.f.: 1 / (1 - 2^1*x / (1 - 2^1*(2^2-1)*x / (1 - 2^5 * x / (1 - 2^3*(2^4-1)*x / (1 - 2^9*x / (1 - 2^5*(2^6-1)*x / ...)))))). - Michael Somos, May 12 2012
a(n) = [x^n] 1/(1 - 2^n*x). - Ilya Gutkovskiy, Oct 10 2017
Sum_{n>=0} 1/a(n) = A319015. - Amiram Eldar, Oct 14 2020
EXAMPLE
G.f. = 1 + 2*x + 16*x^2 + 512*x^3 + 65536*x^4 + 33554432*x^5 + ...
MATHEMATICA
Table[2^(n^2), {n, 0, 15}] (* Vladimir Joseph Stephan Orlovsky, Dec 13 2008 *)
PROG
(PARI) a(n)=polresultant((x-1)^n, (x+1)^n, x) \\ Ralf Stephan
(PARI) a(n)=2^n^2 \\ Charles R Greathouse IV, Jun 23 2021
(Magma) [2^(n^2): n in [0..15]]; // Vincenzo Librandi, May 13 2011
(Sage) [2^(n^2) for n in (0..15)] # G. C. Greubel, Jul 03 2019
(GAP) List([0..15], n-> 2^(n^2) ); # G. C. Greubel, Jul 03 2019
CROSSREFS
KEYWORD
nonn,easy,changed
AUTHOR
STATUS
approved