id:A104011 - OEIS Search Results

Search: id:A104011

Displaying 1-1 of 1 results found.

page 1

Number of prime factors (with multiplicity) of centered dodecahedral numbers (A005904).

+0
2

0, 2, 2, 2, 3, 2, 2, 3, 3, 3, 4, 2, 4, 4, 2, 2, 3, 3, 3, 3, 3, 2, 4, 3, 3, 3, 2, 4, 4, 3, 2, 6, 3, 3, 4, 2, 2, 5, 3, 3, 6, 3, 4, 3, 2, 4, 4, 4, 3, 4, 3, 3, 4, 3, 2, 3, 3, 4, 5, 4, 3, 3, 4, 2, 5, 3, 3, 7, 3, 2, 3, 3, 4, 4, 2, 3, 5, 4, 3, 3, 2, 4, 3, 4, 4, 4, 4, 3, 4, 3, 4, 4, 3, 5, 3, 3, 6, 3, 3, 4 (list; graph; listen)

	OFFSET	`0,2`
	COMMENT	`When a(n) = 2, n is an element of A104012: indices of centered dodecahedral numbers (A005904) which are semiprimes.`
	REFERENCES	`B. K. Teo and N. J. A. Sloane, Magic numbers in polygonal and polyhedral clusters, Inorgan. Chem. 24 (1985), 4545-4558.`
	FORMULA	`a(n) = A001222(A005904(n)). a(n) = Bigomega((2n+1)(5n^2 + 5n + 1)).`
	EXAMPLE	`a(9) = 3 because A005904(9) = 8569 = 11 * 19 * 41, which has 3 prime factors (which happen to have the same number of digits).` `a(18) = 3 because A005904(18) = 63307 = 29 * 37 * 59.` `a(96) = 3 because A005904(96) = 8986273 = 101 * 193 * 461.` `a(126) = 5 because A005904(126) = 20242783 = 11 * 23 * 29 * 31 * 89, which has 5 prime factors (which happen to have the same number of digits).`
	CROSSREFS	`Cf. A001222, A005904, A104012.` `Sequence in context: A129654 A138789 A116504 this_sequence A099774 A048288 A050677` `Adjacent sequences: A104008 A104009 A104010 this_sequence A104012 A104013 A104014`
	KEYWORD	`easy,nonn`
	AUTHOR	`Jonathan Vos Post (jvospost2(AT)yahoo.com), Feb 24 2005`

page 1

Search completed in 0.002 seconds

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

AT&T Labs Research