login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A225987 T(n,k)=Number of pairs of orthogonal (-x,y) vectors of length k*(x+y), where x/y is the n-th rational <= 1, ordered first by y and then x, e.g. 1/1, 1/2, 1/3, 2/3, 1/4, 3/4 ... 19
4, 48, 9, 640, 390, 20, 8960, 20160, 3192, 60, 129024, 1106424, 652784, 48720, 45, 1892352, 62606544, 134432480, 41801760, 26010, 420, 28114944, 3611217792, 28244153600, 36951200000, 21594300, 8168160, 102, 421724160, 211096262400 (list; table; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Table starts

..4....48......640........8960.........129024...........1892352

..9...390....20160.....1106424.......62606544........3611217792

.20..3192...652784...134432480....28244153600.....6052498776192

.60.48720.41801760.36951200000.33792065269760.31520952625612800

.45.26010.21594300.15593341800.11432293516320..8690522384325600

LINKS

R. H. Hardin, Table of n, a(n) for n = 1..1056

EXAMPLE

Some solutions for n=1 k=4

.-1..1....1..1...-1.-1...-1.-1...-1..1....1..1...-1..1...-1.-1...-1.-1...-1..1

..1..1...-1.-1...-1..1...-1..1....1..1...-1..1...-1.-1...-1..1...-1..1...-1.-1

.-1..1...-1..1....1..1...-1.-1...-1..1....1.-1....1.-1...-1.-1....1.-1....1.-1

.-1.-1...-1.-1....1.-1...-1.-1....1..1...-1.-1....1.-1...-1..1....1.-1....1.-1

..1.-1....1.-1...-1.-1....1.-1...-1.-1...-1.-1....1..1...-1..1...-1..1...-1.-1

..1.-1...-1..1....1..1....1..1...-1..1....1.-1....1.-1...-1.-1...-1.-1...-1.-1

..1..1....1..1...-1..1....1.-1....1.-1....1.-1....1..1....1..1...-1.-1...-1.-1

..1..1....1.-1...-1..1...-1..1...-1.-1...-1.-1....1..1....1.-1...-1.-1....1.-1

CROSSREFS

Row 1 is A098402.

Sequence in context: A052105 A010293 A334699 * A178429 A242225 A157818

Adjacent sequences:  A225984 A225985 A225986 * A225988 A225989 A225990

KEYWORD

nonn,tabl

AUTHOR

R. H. Hardin, May 22 2013

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 January 26 23:54 EST 2022. Contains 350601 sequences. (Running on oeis4.)