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A109428
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Numbers n such that sigma(n)/omega(n) is not an integer [sigma(n) =sum of divisors of n; omega(n)=number of distinct prime factors of n].
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1
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18, 36, 50, 72, 84, 98, 100, 144, 156, 162, 196, 200, 225, 228, 242, 252, 273, 288, 300, 324, 336, 338, 364, 372, 392, 399, 400, 441, 444, 468, 484, 516, 525, 532, 576, 578, 624, 648, 651, 676, 684, 700, 722, 732, 741, 756, 777, 784, 800, 804, 819, 868, 876
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| Integers greater than 1 and not in A109427.
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EXAMPLE
| The number 36 is in the sequence because sigma(36)=91 (1+2+3+4+6+9+12+18+36) and omega(36)=2 (2,3) and so sigma(36)/omega(36)=91/2.
The number 12 is not in the sequence because sigma(12)=28 (1+2+3+4+6+12) and omega(12)=2 (2,3) and so sigma(12)/omega(12)=14.
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MAPLE
| with(numtheory): b:=proc(n) if type(sigma(n)/nops(factorset(n)), integer)=false then n else fi end: seq(b(n), n=2..1000);
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CROSSREFS
| Cf. A109427.
Sequence in context: A160844 A040306 A073332 * A166403 A004941 A004961
Adjacent sequences: A109425 A109426 A109427 * A109429 A109430 A109431
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KEYWORD
| nonn
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AUTHOR
| Emeric Deutsch (deutsch(AT)duke.poly.edu), Jun 28 2005
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