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A193644 Number of arrays of -4..4 integers x(1..n) with every x(i) in a subsequence of length 1 or 2 with sum zero. 1
1, 9, 25, 105, 369, 1393, 5105, 18937, 69897, 258521, 955361, 3531745, 13054177, 48254185, 178365177, 659309641, 2437064529, 9008352081, 33298400977, 123083978969, 454966715881, 1681735706553, 6216355687361, 22978092329921 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Column 4 of A193648.

LINKS

R. H. Hardin, Table of n, a(n) for n = 1..200

FORMULA

Empirical: a(n) = 2*a(n-1) +6*a(n-2) +a(n-3).

Empirical g.f.: x*(1 + 7*x + x^2) / (1 - 2*x - 6*x^2 - x^3). - Colin Barker, May 04 2018

EXAMPLE

Some solutions for n=6:

  -2  2 -3 -4  3  3  3  0  0  0 -2 -4  4  4  0  2

   2 -2  3  4 -3 -3 -3  1 -3  4  2  4 -4 -4 -4 -2

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

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

   2  3 -3 -1  3  4 -3 -4 -2  2  2 -3 -4 -2 -3 -3

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

CROSSREFS

Cf. A193648.

Sequence in context: A147475 A146674 A083672 * A083100 A084058 A108570

Adjacent sequences:  A193641 A193642 A193643 * A193645 A193646 A193647

KEYWORD

nonn

AUTHOR

R. H. Hardin, Aug 02 2011

STATUS

approved

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Last modified May 23 12:38 EDT 2019. Contains 323514 sequences. (Running on oeis4.)