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A202069 Number of arrays of n+2 integers in -1..1 with sum zero and the sum of every adjacent pair being odd 2
2, 4, 2, 0, 6, 12, 6, 0, 20, 40, 20, 0, 70, 140, 70, 0, 252, 504, 252, 0, 924, 1848, 924, 0, 3432, 6864, 3432, 0, 12870, 25740, 12870, 0, 48620, 97240, 48620, 0, 184756, 369512, 184756, 0, 705432, 1410864, 705432, 0, 2704156, 5408312, 2704156, 0, 10400600 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Column 1 of A202076

LINKS

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

FORMULA

Empirical: a(n) = f(n mod 4) * binomial(2*z,z), where f(1)=1, f(2)=2, f(3)=1, f(0)=0, and z=floor((n+3)/4)

EXAMPLE

Some solutions for n=10

..0....1...-1....1....0...-1....0....1....1....0....0....0....0...-1....0...-1

..1....0....0....0....1....0...-1....0....0....1...-1....1...-1....0...-1....0

..0...-1...-1...-1....0....1....0....1....1....0....0....0....0....1....0...-1

..1....0....0....0...-1....0....1....0....0...-1...-1....1....1....0....1....0

..0...-1....1...-1....0....1....0...-1....1....0....0....0....0....1....0...-1

..1....0....0....0....1....0....1....0....0....1....1...-1...-1....0....1....0

..0...-1....1....1....0...-1....0....1...-1....0....0....0....0...-1....0....1

.-1....0....0....0....1....0...-1....0....0...-1....1...-1....1....0...-1....0

..0....1....1....1....0....1....0...-1...-1....0....0....0....0...-1....0....1

.-1....0....0....0...-1....0....1....0....0...-1....1....1...-1....0...-1....0

..0....1...-1...-1....0...-1....0...-1...-1....0....0....0....0....1....0....1

.-1....0....0....0...-1....0...-1....0....0....1...-1...-1....1....0....1....0

CROSSREFS

Sequence in context: A277659 A258711 A127278 * A094239 A273240 A201316

Adjacent sequences:  A202066 A202067 A202068 * A202070 A202071 A202072

KEYWORD

nonn

AUTHOR

R. H. Hardin Dec 10 2011

STATUS

approved

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Last modified February 17 20:29 EST 2018. Contains 299297 sequences. (Running on oeis4.)