id:A161506 - OEIS Search Results

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Number of divisors of n that are greater than phi(n)/2, where phi is Euler's totient function.

+0
2

1, 2, 1, 2, 1, 3, 1, 2, 1, 2, 1, 4, 1, 2, 2, 2, 1, 3, 1, 3, 2, 2, 1, 4, 1, 2, 1, 3, 1, 5, 1, 2, 2, 2, 1, 4, 1, 2, 2, 3, 1, 4, 1, 3, 2, 2, 1, 4, 1, 2, 2, 3, 1, 3, 1, 3, 2, 2, 1, 6, 1, 2, 2, 2, 1, 4, 1, 3, 2, 3, 1, 4, 1, 2, 2, 3, 1, 4, 1, 3, 1, 2, 1, 5, 1, 2, 2, 3, 1, 5, 1, 3, 2, 2, 1, 4, 1, 2, 2, 3, 1, 4, 1, 3, 2 (list; graph; listen)

	OFFSET	`1,2`
	COMMENT	`When computing the cyclotomic polynomial Phi(n,x) as the quotient of sparse polynomials (see Arnold and Monagan), the divisors of n greater than phi(n)/2 are not required because only powers up to phi(n)/2 need to be computed; the remaining terms can be inferred because all cyclotomic polynomials are palindromic for n>1. This sequence grows slowly; k first occurs at A161507(k).`
	LINKS	`Andrew Arnold and Michael Monagan Calculating cyclotomic polynomials of very large height`
	MATHEMATICA	`Table[d=Divisors[n]; e=EulerPhi[n]; Length[Select[d, #>e/2&]], {n, 100}]`
	CROSSREFS	`Sequence in context: A062356 A055881 A055874 this_sequence A066451 A091090 A066075` `Adjacent sequences: A161503 A161504 A161505 this_sequence A161507 A161508 A161509`
	KEYWORD	`nonn`
	AUTHOR	`T. D. Noe (noe(AT)sspectra.com), Jun 17 2009`

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Last modified December 8 08:31 EST 2009. Contains 170430 sequences.

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