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A144090
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Triangle read by rows: T(n,k) is the number of partial bijections (or subpermutations) of an n-element set of height k (height(alpha) = |Im(alpha)|) and with exactly 1 fixed point.
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0
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1, 2, 0, 3, 6, 3, 4, 24, 36, 8, 5, 60, 210, 220, 45, 6, 120, 780, 1920, 1590, 264, 7, 210, 2205, 9940, 19005, 12978, 1855, 8, 336, 5208, 37520, 130200, 203952, 118664, 14832, 9, 504, 10836, 114408, 630630, 1783656, 2369556, 1201464, 133497
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OFFSET
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1,2
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LINKS
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FORMULA
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T(n,k) = (n!/(n-k)!)*Sum_{m=0..k-1} ((-1)^m/m!)*C(n-1-m,k-1-m).
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EXAMPLE
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T(3,2) = 6 because there are exactly 6 partial bijections (on a 3-element set) with exactly 1 fixed point and of height 2, namely: (1,2)->(1,3), (1,2)->(3,2), (1,3)->(1,2), (1,3)->(2,3), (2,3)->(2,1), (2,3)->(1,3)- the mappings are coordinate-wise.
First six rows:
1
2 0
3 6 3
4 24 36 8
5 60 210 220 45
6 120 780 1920 1590 264
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MATHEMATICA
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Table[(n!/(n - k)!) Sum[ ((-1)^m/m!) Binomial[n - 1 - m, k - 1 - m], {m, 0, k - 1}], {n, 9}, {k, n}] // Flatten (* Michael De Vlieger, Apr 27 2016 *)
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PROG
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(PARI) T(n, k) = (n!/(n-k)!)*sum(m=0, k-1, ((-1)^m/m!)*binomial(n-1-m, k-1-m));
for (n=1, 10, for (k=1, n, print1(T(n, k), ", "))) \\ Michel Marcus, Apr 27 2016
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CROSSREFS
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KEYWORD
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AUTHOR
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STATUS
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approved
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