id:A081389 - OEIS Search Results

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Number of non-unitary prime divisors of Catalan-numbers, i.e. number of those prime-factors whose exponent is greater than one.

+0
6

0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1, 2, 2, 1, 1, 0, 2, 0, 1, 1, 1, 2, 2, 3, 2, 1, 1, 1, 1, 0, 1, 1, 1, 0, 1, 1, 2, 1, 2, 2, 2, 3, 2, 2, 3, 2, 3, 2, 2, 2, 2, 1, 1, 1, 1, 1, 1, 2, 2, 3, 2, 2, 2, 1, 2, 1, 3, 3, 3, 2, 4, 4, 4, 4, 2, 2, 3, 1, 1, 2, 2, 3, 2, 3, 3, 2, 4, 4, 2, 2, 2, 2, 3, 4, 5, 4, 3, 2, 2, 2, 2, 2, 2, 3 (list; graph; listen)

	OFFSET	`1,13`
	FORMULA	`a(n)=A056170[A000108(n)]`
	EXAMPLE	`n=25: Catalan[25]=C[50,25]/26=4861946401452 =(2.2.3.3.7.7).29.31.37.41.43.47 unitary p-divisors = {29,31,37,41,43,47}, non-unitary ones = {2,3,7}, so a(25)=3/`
	CROSSREFS	`Cf. A000108, A080405, A081386-A081389, A034444, A048105, A056170, A056169.` `Sequence in context: A099918 A099860 A123736 this_sequence A133685 A112183 A119557` `Adjacent sequences: A081386 A081387 A081388 this_sequence A081390 A081391 A081392`
	KEYWORD	`nonn`
	AUTHOR	`Labos E. (labos(AT)ana.sote.hu), Mar 27 2003`

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Last modified August 19 23:53 EDT 2008. Contains 142930 sequences.

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