A007978 - OEIS

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A007978

Least non-divisor of n.

2, 3, 2, 3, 2, 4, 2, 3, 2, 3, 2, 5, 2, 3, 2, 3, 2, 4, 2, 3, 2, 3, 2, 5, 2, 3, 2, 3, 2, 4, 2, 3, 2, 3, 2, 5, 2, 3, 2, 3, 2, 4, 2, 3, 2, 3, 2, 5, 2, 3, 2, 3, 2, 4, 2, 3, 2, 3, 2, 7, 2, 3, 2, 3, 2, 4, 2, 3, 2, 3, 2, 5, 2, 3, 2, 3, 2, 4, 2, 3, 2, 3, 2, 5, 2, 3, 2, 3, 2, 4, 2, 3, 2, 3, 2, 5, 2, 3, 2, 3 (list; graph; refs; listen; history; internal format)

	OFFSET	`1,1`
	COMMENTS	`Least k >= 2 such that sigma(n) divides sigma(n*k), where sigma is A000203 - Benoit Cloitre (benoit7848c(AT)orange.fr), Dec 01 2002` `Contains all and only the prime powers p^k, k>0. The first occurrence of p^k is at A003418(p^k-1); so new records occur at indices in A051451. - Franklin T. Adams-Watters, Jun 13 2011.`
	FORMULA	`a(n) = A053669(n) + A061853(n) = A055874(n) + 1. - Henry Bottomley (se16(AT)btinternet.com), May 10 2001`
	CROSSREFS	`Cf. A003418, A051451, A055874, A053669, A061853.` `Sequence in context: A073820 A103509 A069898 * A096737 A165005 A167530` `Adjacent sequences: A007975 A007976 A007977 * A007979 A007980 A007981`
	KEYWORD	`nonn`
	AUTHOR	`Jeffrey Shallit (shallit(AT)graceland.uwaterloo.ca)`

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Last modified February 15 04:23 EST 2012. Contains 205694 sequences.