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A188237 Number of nondecreasing arrangements of 4 numbers in -(n+2)..(n+2) with sum zero and not more than two numbers equal. 1
15, 30, 52, 81, 121, 172, 234, 311, 403, 510, 636, 781, 945, 1132, 1342, 1575, 1835, 2122, 2436, 2781, 3157, 3564, 4006, 4483, 4995, 5546, 6136, 6765, 7437, 8152, 8910, 9715, 10567, 11466, 12416, 13417, 14469, 15576, 16738, 17955, 19231, 20566, 21960 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Row 4 of A188236.

LINKS

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

FORMULA

Empirical: a(n) = 3*a(n-1) - 3*a(n-2) + 2*a(n-3) - 3*a(n-4) + 3*a(n-5) - a(n-6).

Empirical g.f.: x*(15 - 15*x + 7*x^2 - 15*x^3 + 19*x^4 - 7*x^5) / ((1 - x)^4*(1 + x + x^2)). - Colin Barker, Apr 27 2018

EXAMPLE

Some solutions for n=4:

.-5...-4...-6...-3...-2...-5...-4...-4...-4...-4...-1...-6...-3...-2...-5...-4

.-3....1...-6...-1...-2....0...-1...-1....0...-4....0...-3...-2...-1...-1...-3

..2....1....6....1....0....0....1...-1....0....4....0....3....2....0....3....2

..6....2....6....3....4....5....4....6....4....4....1....6....3....3....3....5

CROSSREFS

Cf. A188236.

Sequence in context: A046046 A330175 A072304 * A190715 A217744 A115811

Adjacent sequences:  A188234 A188235 A188236 * A188238 A188239 A188240

KEYWORD

nonn

AUTHOR

R. H. Hardin, Mar 24 2011

STATUS

approved

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Last modified October 16 15:22 EDT 2021. Contains 348042 sequences. (Running on oeis4.)