A193642 - OEIS

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A193642

Number of arrays of -2..2 integers x(1..n) with every x(i) in a subsequence of length 1 or 2 with sum zero

1, 5, 13, 37, 105, 297, 841, 2381, 6741, 19085, 54033, 152977, 433105, 1226197, 3471581, 9828661, 27826681, 78782265, 223046553, 631484317, 1787844005, 5061703197, 14330578721, 40572407841, 114867676321, 325210747045

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OFFSET

1,2

COMMENTS

Column 2 of A193648

LINKS

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

FORMULA

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

Empirical: G.f.: -x*(1+3*x+x^2) / ( -1+2*x+2*x^2+x^3 ). - R. J. Mathar, Feb 19 2015

EXAMPLE

Some solutions for n=6

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

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

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

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

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

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

CROSSREFS

Sequence in context: A232879 A269803 A298417 * A220709 A182312 A071100

Adjacent sequences: A193639 A193640 A193641 * A193643 A193644 A193645

KEYWORD

nonn

AUTHOR

R. H. Hardin Aug 02 2011

STATUS

approved