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A221235
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Number of nonnegative integer arrays of length n summing to n without adjacent equal values.
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3
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1, 1, 2, 7, 14, 30, 76, 188, 444, 1075, 2656, 6504, 15926, 39316, 97252, 240597, 596686, 1482971, 3689768, 9191590, 22927718, 57253334, 143101896, 358003469, 896391914, 2246149936, 5632310800, 14132640565, 35483595966, 89141668532, 224061612932, 563473301874
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OFFSET
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0,3
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LINKS
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FORMULA
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EXAMPLE
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All solutions for n=3
..1....2....0....2....0....0....1
..2....1....3....0....2....1....0
..0....0....0....1....1....2....2
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MAPLE
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b:= proc(n, h, t) option remember; `if`(t<2, `if`(n<>h, 1, 0),
add(`if`(h=j, 0, b(n-j, `if`(j>n-j, -1, j), t-1)), j=0..n))
end:
a:= n-> b(n, -1, n):
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MATHEMATICA
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b[n_, h_, t_] := b[n, h, t] = If[t < 2, If[n != h, 1, 0],
Sum[If[h == j, 0, b[n-j, If[j > n-j, -1, j], t-1]], {j, 0, n}]];
a[n_] := b[n, -1, n];
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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