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!)
A211473 Number of (n+1)X(n+1) -8..8 symmetric matrices with every 2X2 subblock having sum zero and two, three or four distinct values 1
144, 1224, 10416, 88776, 757784, 6478064, 55460120, 475479800, 4082006352, 35089391112, 301998774840, 2602109942640, 22443946490552, 193770109394072, 1674359497311056, 14479231995139496, 125296349390355480 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Symmetry and 2X2 block sums zero implies that the diagonal x(i,i) are equal modulo 2 and x(i,j)=(x(i,i)+x(j,j))/2*(-1)^(i-j)
LINKS
FORMULA
Empirical: a(n) = 75*a(n-1) -2510*a(n-2) +49200*a(n-3) -622175*a(n-4) +5253075*a(n-5) -29416155*a(n-6) +102987225*a(n-7) -184111448*a(n-8) -476940*a(n-9) +472118829*a(n-10) -56520825*a(n-11) -794496080*a(n-12) -750911850*a(n-13) -339742508*a(n-14) -86830200*a(n-15) -12751696*a(n-16) -999360*a(n-17) -32256*a(n-18)
EXAMPLE
Some solutions for n=3
.-6..3..1..1....5.-6..3.-2...-8..4.-7..4...-5..3..1..3...-1.-2..1.-3
..3..0.-4..2...-6..7.-4..3....4..0..3..0....3.-1.-3.-1...-2..5.-4..6
..1.-4..8.-6....3.-4..1..0...-7..3.-6..3....1.-3..7.-3....1.-4..3.-5
..1..2.-6..4...-2..3..0.-1....4..0..3..0....3.-1.-3.-1...-3..6.-5..7
CROSSREFS
Sequence in context: A235568 A222349 A133062 * A203826 A261655 A203819
KEYWORD
nonn
AUTHOR
R. H. Hardin Apr 12 2012
STATUS
approved

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

License Agreements, Terms of Use, Privacy Policy. .

Last modified February 22 14:47 EST 2024. Contains 370256 sequences. (Running on oeis4.)