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A058730
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Triangle T(n,k) giving number of nonisomorphic simple matroids of rank k on n labeled points (n >= 2, 2 <= k <= n).
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4
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1, 1, 1, 1, 2, 1, 1, 4, 3, 1, 1, 9, 11, 4, 1, 1, 23, 49, 22, 5, 1, 1, 68, 617, 217, 40, 6, 1, 1, 383, 185981, 188936, 1092, 66, 7, 1, 1, 5249, 4884573865
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OFFSET
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2,5
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COMMENTS
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To make this sequence a triangular array, we assume n >= 2 and 2 <= k <= n. According to the references, however, we have T(0,0) = T(1, 1) = 1, and 0 in all other cases. - Petros Hadjicostas, Oct 09 2019
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LINKS
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FORMULA
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T(n, n-1) = n-2 for n >= 2. [Dukes (2004), Lemma 2.2(ii).]
T(n, n-2) = 6 - 4*n + Sum_{k = 1..n} A000041(k) for n >= 3. [Dukes (2004), Lemma 2.2(iv).]
(End)
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EXAMPLE
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Triangle T(n,k) (with rows n >= 2 and columns k >= 2) begins as follows:
1;
1, 1;
1, 2, 1;
1, 4, 3, 1;
1, 9, 11, 4, 1;
1, 23, 49, 22, 5, 1;
1, 68, 617, 217, 40, 6, 1;
1, 383, 185981, 188936, 1092, 66, 7, 1;
...
Matsumoto et al. (2012, p. 36) gave an incomplete row n = 10 (starting at k = 2):
1, 5249, 4884573865, *, 4886374072, 9742, 104, 8, 1;
They also gave incomplete rows for n = 11 and n = 12.
(End)
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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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