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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
OFFSET
1,2
COMMENTS
Column 4 of A193648.
LINKS
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
KEYWORD
nonn
AUTHOR
R. H. Hardin, Aug 02 2011
STATUS
approved