id:A066790 - OEIS Search Results

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a(n) = least natural number k such that the distance between (n, sigma(n)) and (n+k, sigma(n+k)) is an integer (i.e. k^2+(sigma(n+k)-sigma(n))^2 is a square), if such k exists; = 0 otherwise.

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113520, 8, 99585, 44, 5, 5, 48, 10, 280, 3, 45, 3, 2808, 1, 6, 9, 16, 4, 66, 6, 6, 133, 10, 9, 11, 14, 6, 11, 11, 16, 45, 1188, 2, 19, 12, 448, 56, 9, 12, 5, 8, 20, 102, 21, 24, 5, 72, 15, 4, 104 (list; graph; listen)

	OFFSET	`1,1`
	COMMENT	`Is a(n) nonzero for all n?`
	EXAMPLE	`8^2+(sigma(2+8)-sigma(2))^2 = 17^2, and k = 8 is the least natural number achieving this, so a(2) = 8.`
	CROSSREFS	`Sequence in context: A102497 A103113 A122511 this_sequence A135411 A108387 A112009` `Adjacent sequences: A066787 A066788 A066789 this_sequence A066791 A066792 A066793`
	KEYWORD	`nonn`
	AUTHOR	`Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Jan 18 2002`

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Last modified July 25 07:41 EDT 2008. Contains 142293 sequences.

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