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A318391
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Regular triangle where T(n,k) is the number of pairs of set partitions of {1,...,n} with meet of length k.
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12
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1, 1, 3, 1, 9, 15, 1, 21, 90, 113, 1, 45, 375, 1130, 1153, 1, 93, 1350, 7345, 17295, 15125, 1, 189, 4515, 39550, 161420, 317625, 245829, 1, 381, 14490, 192213, 1210650, 4023250, 6883212, 4815403, 1, 765, 45375, 878010, 8014503, 40020750, 113572998, 173354508, 111308699
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OFFSET
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1,3
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LINKS
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FORMULA
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EXAMPLE
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The T(3,2) = 9 pairs of set partitions:
{{1},{2,3}} {{1},{2,3}}
{{1},{2,3}} {{1,2,3}}
{{1,2},{3}} {{1,2},{3}}
{{1,2},{3}} {{1,2,3}}
{{1,3},{2}} {{1,3},{2}}
{{1,3},{2}} {{1,2,3}}
{{1,2,3}} {{1},{2,3}}
{{1,2,3}} {{1,2},{3}}
{{1,2,3}} {{1,3},{2}}
Triangle begins:
1
1 3
1 9 15
1 21 90 113
1 45 375 1130 1153
1 93 1350 7345 17295 15125
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MATHEMATICA
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Table[StirlingS2[n, k]*Sum[StirlingS1[k, i]*BellB[i]^2, {i, k}], {n, 10}, {k, n}]
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PROG
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(PARI) row(n) = {my(b=Vec(serlaplace(exp(exp(x + O(x*x^n))-1)-1))); vector(n, k, stirling(n, k, 2)*sum(i=1, k, stirling(k, i, 1)*b[i]^2))}
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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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