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Search: id:A062385
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| A062385 |
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Numbers n such that sigma(n)-phi(n) is a perfect cube. |
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+0
2
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| 1, 30, 44, 87, 169, 247, 515, 630, 707, 910, 1067, 1255, 1356, 1691, 2128, 2188, 2291, 2438, 2574, 2627, 2747, 2867, 3668, 3689, 4063, 4295, 5206, 5359, 5999, 6331, 6583, 6835, 7719, 8286, 8968, 8991, 9383
(list; graph; listen)
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OFFSET
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1,2
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LINKS
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Harry J. Smith, Table of n, a(n) for n=1,...,1000
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EXAMPLE
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sigma(30)=phi(30) = 72-8 = 64 = 4^3, so 30 is a term of the sequence.
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MATHEMATICA
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Select[Range[10^4], IntegerQ[(DivisorSigma[1, # ] - EulerPhi[ # ])^(1/3)] &]
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PROGRAM
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(PARI) iscube(x)= { if (x==0, return(1)); f=factor(x)~; for(i=1, length(f), if (t=f[2, i]%3, return(0))); return(1); } { n=0; for (m=1, 10^9, if (iscube(sigma(m) - eulerphi(m)), write("b062385.txt", n++, " ", m); if (n==1000, break)) ) } [From Harry J. Smith (hjsmithh(AT)sbcglobal.net), Aug 06 2009]
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CROSSREFS
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Sequence in context: A050776 A090692 A102843 this_sequence A164803 A152569 A114944
Adjacent sequences: A062382 A062383 A062384 this_sequence A062386 A062387 A062388
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KEYWORD
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nonn
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AUTHOR
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Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Feb 13 2002
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