id:A079275 - OEIS Search Results

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Number of divisors of n that are semiprimes with distinct factors.

+0
5

0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1, 0, 1, 1, 0, 0, 1, 0, 1, 1, 1, 0, 1, 0, 1, 0, 1, 0, 3, 0, 0, 1, 1, 1, 1, 0, 1, 1, 1, 0, 3, 0, 1, 1, 1, 0, 1, 0, 1, 1, 1, 0, 1, 1, 1, 1, 1, 0, 3, 0, 1, 1, 0, 1, 3, 0, 1, 1, 3, 0, 1, 0, 1, 1, 1, 1, 3, 0, 1, 0, 1, 0, 3, 1, 1, 1, 1, 0, 3, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 0, 3, 0, 1, 3 (list; graph; listen)

	OFFSET	`1,30`
	COMMENT	`a(A000961(n))=0; a(A007774(n))=1; a(A033992(n))=3; a(A033993(n))=6.`
	FORMULA	`a(n)=omega(n)*(omega(n)-1)/2, where omega(n) is the number of distinct prime factors of n.`
	CROSSREFS	`Cf. A001221, A000005, A006881, A001358.` `Sequence in context: A035655 A036857 A100655 this_sequence A133573 A133574 A151859` `Adjacent sequences: A079272 A079273 A079274 this_sequence A079276 A079277 A079278`
	KEYWORD	`nonn`
	AUTHOR	`Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Feb 07 2003`

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Last modified November 25 20:09 EST 2009. Contains 167514 sequences.

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