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 A199899 Number of -n..n arrays x(0..3) of 4 elements with zero sum, and adjacent elements not both strictly positive and not both strictly negative. 3
 15, 49, 111, 209, 351, 545, 799, 1121, 1519, 2001, 2575, 3249, 4031, 4929, 5951, 7105, 8399, 9841, 11439, 13201, 15135, 17249, 19551, 22049, 24751, 27665, 30799, 34161, 37759, 41601, 45695, 50049, 54671, 59569, 64751, 70225, 75999, 82081, 88479, 95201 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Row 4 of A199898. LINKS R. H. Hardin, Table of n, a(n) for n = 1..200 FORMULA Empirical: a(n) = (4/3)*n^3 + 6*n^2 + (20/3)*n + 1. Conjectures from Colin Barker, Feb 23 2018: (Start) G.f.: x*(3 - x)*(5 - 2*x + x^2) / (1 - x)^4. a(n) = 4*a(n-1) - 6*a(n-2) + 4*a(n-3) - a(n-4) for n>4. (End) EXAMPLE Some solutions for n=6: ..3....3....4...-2....5...-2....5...-3....4...-3....0....2....0....6....3....1 ..0...-6...-4....6...-4....1...-5....2...-5....6....2...-2....5...-1...-5...-5 ..2....3....1...-6....3...-4....3...-1....5....0....0....5...-5....0....6....0 .-5....0...-1....2...-4....5...-3....2...-4...-3...-2...-5....0...-5...-4....4 CROSSREFS Cf. A199898. Sequence in context: A228219 A272039 A241577 * A020257 A298511 A349855 Adjacent sequences: A199896 A199897 A199898 * A199900 A199901 A199902 KEYWORD nonn AUTHOR R. H. Hardin, Nov 11 2011 STATUS approved

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Last modified February 5 12:47 EST 2023. Contains 360084 sequences. (Running on oeis4.)