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A346704
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Product of primes at even positions in the weakly increasing list (with multiplicity) of prime factors of n.
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16
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1, 1, 1, 2, 1, 3, 1, 2, 3, 5, 1, 2, 1, 7, 5, 4, 1, 3, 1, 2, 7, 11, 1, 6, 5, 13, 3, 2, 1, 3, 1, 4, 11, 17, 7, 6, 1, 19, 13, 10, 1, 3, 1, 2, 3, 23, 1, 4, 7, 5, 17, 2, 1, 9, 11, 14, 19, 29, 1, 10, 1, 31, 3, 8, 13, 3, 1, 2, 23, 5, 1, 6, 1, 37, 5, 2, 11, 3, 1, 4, 9
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OFFSET
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1,4
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LINKS
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FORMULA
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EXAMPLE
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The prime factors of 108 are (2,2,3,3,3), with even bisection (2,3), with product 6, so a(108) = 6.
The prime factors of 720 are (2,2,2,2,3,3,5), with even bisection (2,2,3), with product 12, so a(720) = 12.
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MATHEMATICA
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Table[Times@@Last/@Partition[Flatten[Apply[ConstantArray, FactorInteger[n], {1}]], 2], {n, 100}]
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CROSSREFS
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Positions of first appearances are A129597.
The sum of prime indices of a(n) is A346698(n).
A001221 counts distinct prime factors.
A103919 counts partitions by sum and alternating sum (reverse: A344612).
A316524 gives the alternating sum of prime indices (reverse: A344616).
A344606 counts alternating permutations of prime indices.
A344617 gives the sign of the alternating sum of prime indices.
A346633 adds up the even bisection of standard compositions.
Cf. A026424, A035363, A209281, A236913, A342768, A344653, A345957, A345958, A345960, A345961, A345962.
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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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