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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A211333 Number of (n+1)X(n+1) -5..5 symmetric matrices with every 2X2 subblock having sum zero and one, two or three distinct values 1
61, 153, 359, 811, 1825, 4073, 9117, 20435, 46019, 104103, 236721, 541185, 1243505, 2872291, 6664963, 15538035, 36366709, 85451073, 201438293, 476368999, 1129466571, 2684618219, 6394000481, 15257754137, 36465654269, 87277538267 (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

R. H. Hardin, Table of n, a(n) for n = 1..210

FORMULA

Empirical: a(n) = 5*a(n-1) +10*a(n-2) -82*a(n-3) -10*a(n-4) +576*a(n-5) -286*a(n-6) -2266*a(n-7) +1807*a(n-8) +5476*a(n-9) -5310*a(n-10) -8379*a(n-11) +9038*a(n-12) +8059*a(n-13) -9334*a(n-14) -4671*a(n-15) +5778*a(n-16) +1496*a(n-17) -2024*a(n-18) -226*a(n-19) +356*a(n-20) +12*a(n-21) -24*a(n-22)

EXAMPLE

Some solutions for n=3

..0..1..0..0....0..2..1..2....2..1..2..1...-2..1..1..1...-3..1.-3..1

..1.-2..1.-1....2.-4..1.-4....1.-4..1.-4....1..0.-2..0....1..1..1..1

..0..1..0..0....1..1..2..1....2..1..2..1....1.-2..4.-2...-3..1.-3..1

..0.-1..0..0....2.-4..1.-4....1.-4..1.-4....1..0.-2..0....1..1..1..1

CROSSREFS

Sequence in context: A171434 A305172 A316760 * A252811 A252804 A257746

Adjacent sequences:  A211330 A211331 A211332 * A211334 A211335 A211336

KEYWORD

nonn

AUTHOR

R. H. Hardin Apr 07 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 | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified September 17 06:52 EDT 2019. Contains 327119 sequences. (Running on oeis4.)