login
This site is supported by donations to The OEIS Foundation.

 

Logo

Please make a donation to keep the OEIS running. We are now in our 55th year. In the past year we added 12000 new sequences and reached 8000 citations (which often say "discovered thanks to the OEIS"). We need to raise money to hire someone to manage submissions, which would reduce the load on our editors and speed up editing.
Other ways to donate

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A086900 Number of real n X n symmetric (0,1) matrices with positive determinant. 5
1, 1, 5, 338, 14186, 526876, 52658844 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Table of n, a(n) for n=1..7.

Index entries for sequences related to binary matrices

EXAMPLE

For n = 2 the only example is the identity matrix.

MATHEMATICA

triamat[li_List] := Block[{len=Sqrt[8Length[li]+1]/2-1/2}, If[IntegerQ[len], Part[li, # ]& /@ Table[If[j>i, j(j-1)/2+i, i(i-1)/2+j], {i, len}, {j, len}], li]]; Table[it=triamat/@ IntegerDigits[Range[0, -1+2^(n(n+1)/2)], 2, n(n+1)/2]; Count[it, (q_)?MatrixQ/; (Det[q]>0)], {n, 5}]

CROSSREFS

Cf. A086899, A118996.

Sequence in context: A316128 A317434 A029495 * A200002 A265921 A203684

Adjacent sequences:  A086897 A086898 A086899 * A086901 A086902 A086903

KEYWORD

nonn,more

AUTHOR

Wouter Meeussen Aug 23, 2003.

EXTENSIONS

a(6) and a(7) from Giovanni Resta, May 08 2006

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified December 13 22:55 EST 2019. Contains 329974 sequences. (Running on oeis4.)