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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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1
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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
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| 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
| EulerPhi(5313) = 2640 = (2656 + 2624)/2 = (EulerPhi(5314) + EulerPhi(5212))/2
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MATHEMATICA
| Select[ Range[ 2, 10^6 ], EulerPhi[ # ] == (EulerPhi[ #+1 ] + EulerPhi[ #-1 ])/2 & ]
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CROSSREFS
| Sequence in context: A190464 A031660 A031570 * A028549 A093071 A157511
Adjacent sequences: A066164 A066165 A066166 * A066168 A066169 A066170
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KEYWORD
| nonn
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AUTHOR
| Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Dec 13 2001
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EXTENSIONS
| 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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