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Search: id:A066167
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| A066167 |
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Numbers n such that EulerPhi(n) = (EulerPhi(n+1) + EulerPhi(n-1))/2. |
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+0
2
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| 5187, 5313, 273525, 292005, 494715, 536055, 657855, 2379975, 3045075, 9960045, 15091545, 19420665, 23977305, 28292745, 45864225, 62361495, 81758325, 93794715, 213205575, 309227655, 602444325, 806687427, 1375738845, 1411639047, 1589814975, 1628145057
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OFFSET
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1,1
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COMMENT
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Identical to the sequence of n such that EulerPhi(n-1), EulerPhi(n), EulerPhi(n+1) are in arithmetic progression.
3 divides all known terms (up to 2*10^9 ) of the sequence. - Farideh Firoozbakht (mymontain(AT)yahoo.com), Jan 01 2008
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EXAMPLE
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EulerPhi(5313) = 2640 = (2656 + 2624)/2 = (EulerPhi(5314) + EulerPhi(5212))/2
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MATHEMATICA
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Select[ Range[ 2, 10^6 ], EulerPhi[ # ] == (EulerPhi[ #+1 ] + EulerPhi[ #-1 ])/2 & ]
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CROSSREFS
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Sequence in context: A061050 A031660 A031570 this_sequence A028549 A093071 A109159
Adjacent sequences: A066164 A066165 A066166 this_sequence A066168 A066169 A066170
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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), Dec 13 2001
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EXTENSIONS
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More terms from Labos E. (labos(AT)ana.sote.hu), Oct 27 2004
More terms from Farideh Firoozbakht (mymontain(AT)yahoo.com), Jan 01 2008
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