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A193695
Number of arrays of -1..1 integers x(1..n) with every x(i) in a subsequence of length 1, 2 or 3 with sum zero
2
1, 3, 9, 23, 57, 141, 351, 875, 2181, 5435, 13543, 33747, 84093, 209549, 522169, 1301177, 3242363, 8079545, 20133171, 50169233, 125015177, 311521495, 776270883, 1934365665, 4820186623, 12011275583, 29930530167, 74582972465, 185851027385
OFFSET
1,2
COMMENTS
Column 1 of A193702
LINKS
FORMULA
Empirical: a(n) = 2*a(n-1) +a(n-2) +a(n-4) +a(n-5).
Empirical: G.f.: x*( -1-x-2*x^2-2*x^3-x^4 ) / ( -1+2*x+x^2+x^4+x^5 ). - R. J. Mathar, Feb 19 2015
EXAMPLE
Some solutions for n=6
.-1....0....1....0....0....0....0....0....1...-1....1....1....0....1...-1....0
..1...-1...-1....0....0....0...-1....1...-1....1...-1...-1....0...-1....1...-1
..0....1....1....0....1....0....0...-1....0....1....1....1....1....1...-1....1
..0....0....1....1....0...-1....1....0....0...-1...-1....0...-1...-1....0...-1
..1...-1...-1...-1...-1....1....1....0....1....0....1....0....0....0....1....1
.-1....0....0....1....1....0...-1....0...-1....0...-1....0....0....1...-1....0
CROSSREFS
Sequence in context: A045883 A292329 A133654 * A226845 A096574 A045650
KEYWORD
nonn
AUTHOR
R. H. Hardin Aug 02 2011
STATUS
approved