id:A078593 - OEIS Search Results

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Number of pairs (x,y) 1<=x<=y<=n such that 1/x+1/y+1/n < 1/2.

+0
1

0, 0, 0, 0, 0, 0, 4, 9, 16, 24, 33, 42, 55, 68, 81, 96, 111, 127, 145, 163, 183, 203, 224, 246, 270, 294, 319, 345, 372, 400, 429, 459, 490, 522, 555, 589, 624, 660, 697, 735, 774, 814, 856, 898, 941, 985, 1030, 1076, 1123, 1171, 1220, 1270, 1321, 1373, 1426 (list; graph; listen)

	OFFSET	`1,7`
	FORMULA	`for n>=43 a(n) = (1/2)(n^2 - 3n - 8 )`
	PROGRAM	`(PARI) a(n)=sum(i=1, n, sum(j=1, i, if(sign(1/i+1/j+1/n-1/2)+1, 0, 1)))`
	CROSSREFS	`Sequence in context: A139588 A122986 A066427 this_sequence A052117 A033611 A033615` `Adjacent sequences: A078590 A078591 A078592 this_sequence A078594 A078595 A078596`
	KEYWORD	`nonn`
	AUTHOR	`Benoit Cloitre (benoit7848c(AT)orange.fr), Dec 08 2002`

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Last modified July 24 12:00 EDT 2008. Contains 142294 sequences.

AT&T Labs Research