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Unitary untouchable numbers of second kind: numbers n such that usigma(x)=n has no solution, where usigma(x) (A034448) is the sum of unitary divisors of x.

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2, 7, 11, 13, 15, 16, 19, 21, 22, 23, 25, 27, 29, 31, 34, 35, 37, 39, 41, 43, 45, 46, 47, 49, 51, 52, 53, 55, 57, 58, 59, 61, 63, 64, 66, 67, 69, 71, 73, 75, 76, 77, 79, 81, 83, 85, 86, 87, 88, 89, 91, 92, 93, 94, 95, 97, 99, 101, 103, 105, 106, 107, 109, 111, 113, 115, 116 (list; graph; listen)

	OFFSET	`1,1`
	FORMULA	`Suppose usigma(x)=n. Then by definition usigma(x)=n>1 for n>1. Let be x a prime. Then usigma(x)=x+1 and so n=x+1. For x not prime of course x+1<n. So in general x<=n-1.`
	CROSSREFS	`Cf. A063948, A034448.` `Sequence in context: A113544 A045173 A063976 this_sequence A069180 A020627 A043292` `Adjacent sequences: A063997 A063998 A063999 this_sequence A064001 A064002 A064003`
	KEYWORD	`easy,nonn`
	AUTHOR	`Labos E. (labos(AT)ana.sote.hu) and Felice Russo (felice.russo(AT)katamail.com), Sep 05 2001`
	EXTENSIONS	`Edited by njas, May 04 2007`

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

AT&T Labs Research