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A305565
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Regular triangle where T(n,k) is the number of finite sets of positive integers with least common multiple n and greatest common divisor k.
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4
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1, 1, 1, 1, 0, 1, 2, 1, 0, 1, 1, 0, 0, 0, 1, 7, 1, 1, 0, 0, 1, 1, 0, 0, 0, 0, 0, 1, 4, 2, 0, 1, 0, 0, 0, 1, 2, 0, 1, 0, 0, 0, 0, 0, 1, 7, 1, 0, 0, 1, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 32, 7, 2, 1, 0, 1, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0
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OFFSET
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1,7
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LINKS
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FORMULA
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If k divides n then T(n,k) = T(n/k,1) = A305564(n/k); otherwise T(n,k) = 0.
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EXAMPLE
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The T(12,2) = 7 sets are {2,12}, {4,6}, {2,4,6}, {2,4,12}, {2,6,12}, {4,6,12}, {2,4,6,12}.
Triangle begins:
1
1 1
1 0 1
2 1 0 1
1 0 0 0 1
7 1 1 0 0 1
1 0 0 0 0 0 1
4 2 0 1 0 0 0 1
2 0 1 0 0 0 0 0 1
7 1 0 0 1 0 0 0 0 1
1 0 0 0 0 0 0 0 0 0 1
32 7 2 1 0 1 0 0 0 0 0 1
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MATHEMATICA
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Table[Length[Select[Subsets[Divisors[n]], And[GCD@@#==k, LCM@@#==n]&]], {n, 20}, {k, n}]
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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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