id:A131902 - OEIS Search Results

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A131902

Smallest positive integer k with the same sum of divisors as the n-th integer for which such a k exists.

+0
7

6, 14, 10, 14, 16, 20, 21, 33, 24, 28, 20, 30, 33, 30, 34, 30, 54, 40, 24, 42, 44, 42, 66, 30, 48, 42, 60, 57, 68, 44, 54, 40, 60, 66, 54, 52, 63, 85, 102, 74, 66, 104, 88, 66, 80, 60, 84, 99, 93, 96, 86, 114, 76, 132, 105, 102, 60, 88, 111, 90, 138, 105, 114, 102, 105, 138, 96 (list; graph; listen)

	OFFSET	`1,1`
	FORMULA	`Let S={n>0 : there exists a k>0 and k<n with sigma(k)=sigma(n)}. Then a(n):=min(k>0: sigma(k)=sigma(n-th element of S)`
	EXAMPLE	`a(3)=10 because 17 is the third integer for which a smaller integer with same sum of divisors exists and sigma(17)=1+17=18 and sigma(10)=1+2+5+10=18 and there is no k>0 less than 10 with sigma(k)=18`
	MATHEMATICA	`Clear[tmp]; Function[n, If[Head[ #1]===tmp, #1=n; Unevaluated[Sequence[]], #1]& [tmp[DivisorSigma[1, n]]]]/@Range[200]`
	CROSSREFS	`Cf. A069822, A131903 - A131908.` `Sequence in context: A042285 A041070 A065938 this_sequence A079010 A015822 A023883` `Adjacent sequences: A131899 A131900 A131901 this_sequence A131903 A131904 A131905`
	KEYWORD	`easy,nonn`
	AUTHOR	`Peter Pein (petsie(AT)dordos.net), Jul 26 2007`

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Last modified November 30 13:13 EST 2009. Contains 167758 sequences.

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