id:A080756 - OEIS Search Results

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A positive integer n is in this sequence if it has infinitely many multiples that have exactly n positive divisors each.

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8, 9, 12, 16, 18, 20, 24, 25, 27, 28, 32, 36, 40, 44, 45, 48, 49, 50, 52, 54, 56, 60, 63, 64, 68, 72, 75, 76, 80, 81, 84, 88, 90, 92, 96, 98, 99, 100, 104, 108, 112, 116, 117, 120, 121, 124, 125, 126, 128, 132, 135, 136, 140, 144, 147, 148, 150, 152, 153, 156, 160 (list; graph; listen)

	OFFSET	`0,1`
	COMMENT	`Regional Math Competition for Northwestern Bulgaria, Vraca 2003, Problem 12/3`
	FORMULA	`All non-square-free positive integers except the number 4.`
	EXAMPLE	`a(0)=8 because all numbers of the type 2^3p (p-odd prime) have exactly 8 divisors and are multiples of 8. Any square-free number has only finite number of such multiples. The number 4 has only one such multiple (8).`
	CROSSREFS	`Cf. A013929.` `Sequence in context: A120176 A048590 A131864 this_sequence A063080 A167131 A109079` `Adjacent sequences: A080753 A080754 A080755 this_sequence A080757 A080758 A080759`
	KEYWORD	`nonn`
	AUTHOR	`Ivaylo Kortezov (kortezov(AT)math.bas.bg), Mar 09 2003`

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Last modified November 25 08:46 EST 2009. Contains 167481 sequences.

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