login
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
OFFSET
1,1
COMMENTS
Row 4 of A188236.
LINKS
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
KEYWORD
nonn
AUTHOR
R. H. Hardin, Mar 24 2011
STATUS
approved