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A131902
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Smallest positive integer k with the same sum of divisors as the n-th integer for which such a k exists.
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6
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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; refs; listen; history; internal format)
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OFFSET
| 1,1
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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)
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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
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MATHEMATICA
| Clear[tmp]; Function[n, If[Head[ #1]===tmp, #1=n; Unevaluated[Sequence[]], #1]& [tmp[DivisorSigma[1, n]]]]/@Range[200]
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CROSSREFS
| Cf. A069822, A131903 - A131908.
Sequence in context: A201449 A205300 A065938 * A184998 A079010 A015822
Adjacent sequences: A131899 A131900 A131901 * A131903 A131904 A131905
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KEYWORD
| easy,nonn
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AUTHOR
| Peter Pein (petsie(AT)dordos.net), Jul 26 2007
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