id:A073542 - OEIS Search Results

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Numbers n such that 1/(1/phi(n) + 1/phi(n+1)) is an integer.

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3, 12, 13, 15, 35, 36, 37, 55, 61, 72, 73, 86, 90, 96, 99, 104, 108, 119, 126, 154, 157, 164, 175, 182, 192, 193, 194, 244, 255, 277, 286, 296, 304, 313, 352, 362, 364, 369, 378, 397, 421, 432, 455, 457, 483, 495, 515, 527, 541, 545, 560, 576, 584, 602, 609 (list; graph; listen)

	OFFSET	`1,1`
	FORMULA	`Is a(n) asymptotic to c*n^(3/2) with 1<c<1.5?`
	EXAMPLE	`1/phi(286)+1/phi(287) = 1/120+1/240 = 1/80 so 286 is in the sequence.`
	MATHEMATICA	`Select[Range[700], IntegerQ[1/(1/EulerPhi[ # ]+1/EulerPhi[ #+1])]&]`
	CROSSREFS	`Sequence in context: A070732 A085060 A024546 this_sequence A063444 A117061 A089919` `Adjacent sequences: A073539 A073540 A073541 this_sequence A073543 A073544 A073545`
	KEYWORD	`easy,nonn`
	AUTHOR	`Benoit Cloitre (benoit7848c(AT)orange.fr), Aug 27 2002`
	EXTENSIONS	`Edited by Dean Hickerson (dean.hickerson(AT)yahoo.com), Aug 31 2002`

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Last modified December 2 11:54 EST 2009. Contains 167921 sequences.

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