Search: a331639 -id:a331639
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A331277
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Array read by antidiagonals: A(n,k) is the number of binary matrices with k distinct columns and any number of nonzero rows with n ones in every column and columns in decreasing lexicographic order.
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+10
5
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1, 1, 1, 0, 1, 1, 0, 1, 1, 1, 0, 1, 6, 1, 1, 0, 1, 62, 31, 1, 1, 0, 1, 900, 2649, 160, 1, 1, 0, 1, 16824, 441061, 116360, 841, 1, 1, 0, 1, 384668, 121105865, 231173330, 5364701, 4494, 1, 1, 0, 1, 10398480, 49615422851, 974787170226, 131147294251, 256452714, 24319, 1, 1
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OFFSET
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0,13
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COMMENTS
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The condition that the columns be in decreasing order is equivalent to considering nonequivalent matrices with distinct columns up to permutation of columns.
A(n,k) is the number of labeled n-uniform hypergraphs with k edges and no isolated vertices. When n=2 these objects are graphs.
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LINKS
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FORMULA
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A(n, k) = Sum_{j=0..n*k} binomial(binomial(j,n),k) * (Sum_{i=j..n*k} (-1)^(i-j)*binomial(i,j)).
A(n, k) = Sum_{j=0..k} Stirling1(k, j)*A262809(n, j)/k!.
A(n, k) = Sum_{j=0..k} (-1)^(k-j)*binomial(k-1, k-j)*A330942(n, j).
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EXAMPLE
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Array begins:
====================================================================
n\k | 0 1 2 3 4 5 6
----+---------------------------------------------------------------
0 | 1 1 0 0 0 0 0 ...
1 | 1 1 1 1 1 1 1 ...
2 | 1 1 6 62 900 16824 384668 ...
3 | 1 1 31 2649 441061 121105865 49615422851 ...
4 | 1 1 160 116360 231173330 974787170226 ...
5 | 1 1 841 5364701 131147294251 ...
6 | 1 1 4494 256452714 78649359753286 ...
...
The A(2,2) = 6 matrices are:
[1 0] [1 0] [1 0] [1 1] [1 0] [1 0]
[1 0] [0 1] [0 1] [1 0] [1 1] [0 1]
[0 1] [1 0] [0 1] [0 1] [0 1] [1 1]
[0 1] [0 1] [1 0]
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PROG
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(PARI) T(n, k)={my(m=n*k); sum(j=0, m, binomial(binomial(j, n), k)*sum(i=j, m, (-1)^(i-j)*binomial(i, j)))}
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CROSSREFS
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The version with nonnegative integer entries is A331278.
The version with not necessarily distinct columns is A330942.
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KEYWORD
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AUTHOR
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STATUS
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approved
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A331638
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Number of binary matrices with nonzero rows, a total of n ones and each column with the same number of ones and columns in nonincreasing lexicographic order.
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+10
2
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1, 3, 5, 16, 17, 140, 65, 1395, 2969, 22176, 1025, 1050766, 4097, 13010328, 128268897, 637598438, 65537, 64864962683, 262145, 1676258452736, 28683380484257, 24908619669860, 4194305, 30567710172480050, 8756434134071649, 62128557507554504, 21271147396968151093
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graph;
refs;
listen;
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OFFSET
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1,2
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COMMENTS
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The condition that the columns be in nonincreasing order is equivalent to considering nonequivalent matrices up to permutation of columns.
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LINKS
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FORMULA
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a(p) = 2^(p-1) + 1 for prime p.
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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