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A120499
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Irregular triangle read by rows in which the n-th row consists of the positive integers which are <= n and divisible by exactly one prime dividing n (but are coprime to every other prime dividing n). (a(1) = 1).
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4
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1, 2, 3, 2, 4, 5, 2, 3, 4, 7, 2, 4, 6, 8, 3, 6, 9, 2, 4, 5, 6, 8, 11, 2, 3, 4, 8, 9, 10, 13, 2, 4, 6, 7, 8, 10, 12, 3, 5, 6, 9, 10, 12, 2, 4, 6, 8, 10, 12, 14, 16, 17, 2, 3, 4, 8, 9, 10, 14, 15, 16, 19, 2, 4, 5, 6, 8, 12, 14, 15, 16, 18, 3, 6, 7, 9, 12, 14, 15, 18, 2, 4, 6, 8, 10, 11, 12, 14, 16, 18
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OFFSET
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1,2
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COMMENTS
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n-th row of array has A116512(n) terms.
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LINKS
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EXAMPLE
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12 is divisible by the primes 2 and 3. 2,3,4,8,9,10 are those positive integers which are <= 12, which are divisible by 2 or 3, but are not divisible by 2 and 3. So the 12th row of the array is {2,3,4,8,9,10}.
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MATHEMATICA
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Table[Select[Range@ n, Function[k, Total@ Boole@ Map[Divisible[k, #] &, FactorInteger[n][[All, 1]]] == 1]], {n, 22}] // Flatten (* Michael De Vlieger, Sep 30 2017 *)
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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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EXTENSIONS
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STATUS
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approved
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