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Search: id:A056675
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| A056675 |
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Number of non-unitary but square-free divisors of n!. Also number of unitary but not-square-free divisors of n!. |
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+0
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| 0, 0, 0, 2, 4, 6, 12, 12, 12, 14, 28, 28, 56, 60, 60, 60, 120, 120, 240, 240, 240, 248, 496, 496, 496, 504, 504, 504, 1008, 1008, 2016, 2016, 2016, 2032, 2032, 2032, 4064, 4080, 4080, 4080, 8160, 8160, 16320, 16320, 16320, 16352, 32704, 32704, 32704, 32704
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OFFSET
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1,4
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FORMULA
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a(n) = A048656 - A000005[A055231(n!)] = A048656 - A000005[A007913(n!)/A055229(n!)]
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EXAMPLE
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n=10, 10!=2.2.2.2.2.2.2.2.3.3.3.3.5.5.7=256.81.25.7, it has 270 divisors,16 unitary and 16 are square-free; overlap={1,7}.Set {2,3,5,6,10,14,15,21,30,35,42,70,105,210} represents the square-free not-unitary divisors of 10!, so a(10)=14.
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CROSSREFS
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A048656, A000005, A055231, A007913, A055229, A000142.
Adjacent sequences: A056672 A056673 A056674 this_sequence A056676 A056677 A056678
Sequence in context: A057700 A136103 A053146 this_sequence A062857 A061799 A076868
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KEYWORD
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nonn
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AUTHOR
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Labos E. (labos(AT)ana.sote.hu), Aug 10 2000
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