id:A015614 - OEIS Search Results

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Sum( phi(i), i=1..n) - 1.

+0
7

0, 1, 3, 5, 9, 11, 17, 21, 27, 31, 41, 45, 57, 63, 71, 79, 95, 101, 119, 127, 139, 149, 171, 179, 199, 211, 229, 241, 269, 277, 307, 323, 343, 359, 383, 395, 431, 449, 473, 489, 529, 541, 583, 603, 627, 649, 695, 711, 753, 773, 805, 829, 881, 899, 939, 963 (list; graph; listen)

	OFFSET	`1,3`
	COMMENT	`Number of elements in the set {(x,y): 1<=x<y<=n, 1=gcd(x,y)}; number of fractions in (Haros)-Farey series of order n.` `a(n) = (A018805(n) - 1)/2. - Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Apr 08 2006`
	CROSSREFS	`Equals A002088[ n ] - 1.` `Sequence in context: A056533 A114186 A117992 this_sequence A138203 A007952 A145819` `Adjacent sequences: A015611 A015612 A015613 this_sequence A015615 A015616 A015617`
	KEYWORD	`nonn`
	AUTHOR	`Olivier Gerard (olivier.gerard(AT)gmail.com)`
	EXTENSIONS	`More terms from Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Apr 08 2006`

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Last modified November 24 23:16 EST 2009. Contains 167481 sequences.

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