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A124327
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Triangle read by rows: T(n,k) is the number of partitions of the set {1,2,...,n} such that the sum of the least entries of the blocks is k (1<=k<=n*(n+1)/2).
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8
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1, 1, 0, 1, 1, 0, 2, 1, 0, 1, 1, 0, 4, 2, 1, 3, 2, 1, 0, 1, 1, 0, 8, 4, 2, 10, 6, 7, 2, 5, 3, 2, 1, 0, 1, 1, 0, 16, 8, 4, 29, 19, 21, 14, 23, 14, 18, 10, 7, 7, 5, 3, 2, 1, 0, 1, 1, 0, 32, 16, 8, 85, 56, 64, 42, 101, 62, 75, 69, 47, 54, 38, 38, 24, 23, 10, 13, 7, 5, 3, 2, 1, 0, 1, 1, 0, 64, 32, 16
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OFFSET
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1,7
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COMMENTS
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Row n has n(n+1)/2 terms. Row sums yield the Bell numbers (A000110). T(n,1)=1; T(n,2)=0; T(n,3)=2^(n-2). for n>=2; T(n,4)=2^(n-3) for n>=3; T(n,5)=2^(n-4) for n>=4.
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LINKS
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FORMULA
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The generating polynomial of row n is P(n,t)=Q(n,t,1), where Q(n,t,s)=s*dQ(n-1,t,s)/ds + st^n*Q(n-1,t,s); Q(1,t,s)=ts.
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EXAMPLE
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T(4,7) = 2 because we have 13|2|4 and 1|23|4.
Triangle starts:
1;
1, 0, 1;
1, 0, 2, 1, 0, 1;
1, 0, 4, 2, 1, 3, 2, 1, 0, 1;
1, 0, 8, 4, 2, 10, 6, 7, 2, 5, 3, 2, 1, 0, 1;
1, 0, 16, 8, 4, 29, 19, 21, 14, 23, 14, 18, 10, 7, 7, 5, 3, 2, 1, 0, 1;
...
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MAPLE
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Q[1]:=t*s: for n from 2 to 8 do Q[n]:=expand(s*diff(Q[n-1], s)+t^n*s*Q[n-1]) od: for n from 1 to 8 do P[n]:=sort(subs(s=1, Q[n])) od: for n from 1 to 8 do seq(coeff(P[n], t, k), k=1..n*(n+1)/2) od; # yields sequence in triangular form
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CROSSREFS
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KEYWORD
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nonn,tabf
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AUTHOR
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STATUS
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approved
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