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A211470 Number of (n+1)X(n+1) -8..8 symmetric matrices with every 2X2 subblock having sum zero and one, two or three distinct values 1
145, 397, 945, 2153, 4775, 10527, 22995, 50565, 110915, 245927, 545909, 1225707, 2760503, 6282475, 14352999, 33082005, 76545031, 178364381, 417062331, 980496727, 2311774857, 5472654325, 12985260305, 30901798587, 73669894089 (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) = 6*a(n-1) +14*a(n-2) -144*a(n-3) -12*a(n-4) +1553*a(n-5) -1086*a(n-6) -9957*a(n-7) +11142*a(n-8) +42330*a(n-9) -59054*a(n-10) -126094*a(n-11) +201376*a(n-12) +271448*a(n-13) -474492*a(n-14) -430008*a(n-15) +794866*a(n-16) +506763*a(n-17) -953966*a(n-18) -447303*a(n-19) +814746*a(n-20) +296554*a(n-21) -485322*a(n-22) -146850*a(n-23) +194433*a(n-24) +52926*a(n-25) -49234*a(n-26) -13004*a(n-27) +7010*a(n-28) +1900*a(n-29) -420*a(n-30) -120*a(n-31)

EXAMPLE

Some solutions for n=3

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

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

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

..4.-2..4.-7...-2..0..0..2...-2..2.-2..2....0..1..0..2...-1..0..1.-1

CROSSREFS

Sequence in context: A094613 A207058 A116208 * A031702 A297732 A296972

Adjacent sequences:  A211467 A211468 A211469 * A211471 A211472 A211473

KEYWORD

nonn

AUTHOR

R. H. Hardin Apr 12 2012

STATUS

approved

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Last modified September 23 11:53 EDT 2020. Contains 337310 sequences. (Running on oeis4.)