id:A067780 - OEIS Search Results

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Numbers n such that sigma(n)/phi(n) is prime.

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2, 3, 12, 15, 35, 56, 78, 140, 190, 357, 630, 812, 910, 1045, 1672, 2214, 2580, 3339, 4180, 4522, 4674, 5049, 5278, 5544, 8008, 10659, 11160, 12441, 16065, 16120, 16770, 18630, 18810, 24244, 24871, 24969, 25070, 25758, 27000, 27170, 28896 (list; graph; listen)

	OFFSET	`1,1`
	EXAMPLE	`sigma(12)/phi(12) = 28/4 = 7, a prime, so 12 is a term of the sequence.`
	MATHEMATICA	`Select[Range[10^5], PrimeQ[DivisorSigma[1, # ]/EulerPhi[ # ]] &]`
	CROSSREFS	`Sequence in context: A015756 A090512 A076175 this_sequence A124486 A123761 A047163` `Adjacent sequences: A067777 A067778 A067779 this_sequence A067781 A067782 A067783`
	KEYWORD	`nonn`
	AUTHOR	`Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Feb 06 2002`

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

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