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Search: id:A131906
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| A131906 |
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Smallest positive integer k with the same sum of squares of divisors as the n-th integer for which such a k exists. |
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+0
1
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| 6, 24, 30, 40, 66, 78, 102, 120, 114, 120, 136, 138, 150, 168, 174, 186, 186, 230, 222, 280, 264, 246, 258, 280, 318, 330, 354, 360, 366, 430, 408, 390, 402, 408, 456, 426
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OFFSET
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1,1
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FORMULA
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a(n)=min(k>0, k has the same sum of squares of divisors as A131905(n))
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EXAMPLE
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a(5)=66 because A131905(5)=77 and the sum of the squares of the divisors of 77 is 1+49+121+5929=6100 and the sum of the squares of the divisors of 66 is 1+4+9+36+121+484+1089+4356=6100 and there is no smaller positive integer with this squaresum of its divisors
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MATHEMATICA
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Clear[tmp]; Last@Transpose[ Function[n, (If[Head[ #1] === tmp, #1 = n; Unevaluated[Sequence[]], {n, #1}] & )[tmp[DivisorSigma[2, n]]]] /@ Range[500]]
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CROSSREFS
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Cf. A069822, A131902-A131908.
Sequence in context: A064510 A114274 A110926 this_sequence A046131 A009111 A009112
Adjacent sequences: A131903 A131904 A131905 this_sequence A131907 A131908 A131909
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KEYWORD
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easy,nonn
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AUTHOR
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Peter Pein (petsie(AT)dordos.net), Jul 26 2007
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