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A064580
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Triangle associated with rooted trees with a degree constraint (A036765).
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5
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1, 1, 1, 1, 2, 2, 1, 3, 5, 5, 1, 4, 9, 14, 13, 1, 5, 14, 28, 40, 36, 1, 6, 20, 48, 87, 118, 104, 1, 7, 27, 75, 161, 273, 357, 309, 1, 8, 35, 110, 270, 536, 866, 1100, 939, 1, 9, 44, 154, 423, 951, 1782, 2772, 3441, 2905, 1, 10, 54, 208, 630, 1572, 3310, 5928, 8946, 10900, 9118
(list;
table;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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0,5
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COMMENTS
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LINKS
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FORMULA
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a(n, k) = a(n-1, k) + a(n-1, k-1) + a(n-1, k-2) + a(n-1, k-3) with a(0, 0)=1 and a(n, k)=0 if n < k or k < 0.
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EXAMPLE
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Triangle begins:
1;
1, 1;
1, 2, 2;
1, 3, 5, 5;
1, 4, 9, 14, 13;
1, 5, 14, 28, 40, 36;
...
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MATHEMATICA
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a[n_, k_] /; 0 <= k <= n = a[n, k] = a[n - 1, k] + a[n - 1, k - 1] + a[n - 1, k - 2] + a[n - 1, k - 3]; a[0, 0] = 1; a[_, _] = 0;
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PROG
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(Sage) # uses[riordan_array from A256893]
M = riordan_array(1, x/(1+x+x^2+x^3), 12).inverse()
for m in M[1:]:
print([r for r in reversed(list(m)) if r != 0]) # Peter Luschny, Aug 17 2016
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CROSSREFS
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KEYWORD
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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