id:A109427 - OEIS Search Results

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Numbers n such that sigma(n)/omega(n) is an integer [sigma(n) =sum of divisors of n; omega(n)=number of distinct prime factors of n].

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2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 73, 74, 75, 76, 77 (list; graph; listen)

	OFFSET	`1,1`
	COMMENT	`Integers greater than 1 and not in A109428.`
	EXAMPLE	`The number 12 is 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.` `The number 36 is not 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.`
	MAPLE	`with(numtheory): a:=proc(n) if type(sigma(n)/nops(factorset(n)), integer)=true then n else fi end: seq(a(n), n=2..90);`
	CROSSREFS	`Cf. A109428.` `Sequence in context: A080681 A076084 A093618 this_sequence A098451 A098452 A088382` `Adjacent sequences: A109424 A109425 A109426 this_sequence A109428 A109429 A109430`
	KEYWORD	`nonn`
	AUTHOR	`Emeric Deutsch (deutsch(AT)duke.poly.edu), Jun 28 2005`

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Last modified July 23 17:35 EDT 2008. Contains 142285 sequences.

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