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Search: id:A109424
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| A109424 |
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Numbers n such that sigma(n)/bigomega(n) is not an integer [sigma(n) =sum of divisors of n; bigomega(n)=number of prime divisors of n, counted with multiplicity]. |
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+0
2
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| 4, 9, 12, 16, 25, 27, 28, 32, 36, 40, 48, 49, 52, 63, 64, 75, 76, 80, 81, 90, 100, 104, 112, 117, 121, 124, 128, 136, 144, 148, 162, 169, 171, 172, 175, 176, 180, 192, 196, 208, 225, 232, 234, 243, 244, 252, 256, 268, 272, 273, 279, 289, 292, 296, 300, 306, 316
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Integers greater than 1 and not in A109423.
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EXAMPLE
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The number 12 is in the sequence because sigma(12)=28 (1+2+3+4+6+12) and bigomega(12)=3 (2,2,3) and so sigma(12)/bigomega(12)=28/3.
The number 24 is not in the sequence because sigma(24)=60 (1+2+3+4+6+8+12+24) and bigomega(24)=4 (2,2,2,3) and so sigma(24)/bigomega(24)=15.
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MAPLE
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with(numtheory): b:=proc(n) if type(sigma(n)/bigomega(n), integer)=false then n else fi end: seq(b(n), n=2..340);
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CROSSREFS
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Cf. A109423.
Sequence in context: A045673 A034032 A141037 this_sequence A034019 A034018 A047461
Adjacent sequences: A109421 A109422 A109423 this_sequence A109425 A109426 A109427
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KEYWORD
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nonn
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AUTHOR
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Emeric Deutsch (deutsch(AT)duke.poly.edu), Jun 28 2005
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