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A073542
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Numbers n such that 1/(1/phi(n) + 1/phi(n+1)) is an integer.
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0
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3, 12, 13, 15, 35, 36, 37, 55, 61, 72, 73, 86, 90, 96, 99, 104, 108, 119, 126, 154, 157, 164, 175, 182, 192, 193, 194, 244, 255, 277, 286, 296, 304, 313, 352, 362, 364, 369, 378, 397, 421, 432, 455, 457, 483, 495, 515, 527, 541, 545, 560, 576, 584, 602, 609
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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FORMULA
| Is a(n) asymptotic to c*n^(3/2) with 1<c<1.5?
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EXAMPLE
| 1/phi(286)+1/phi(287) = 1/120+1/240 = 1/80 so 286 is in the sequence.
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MATHEMATICA
| Select[Range[700], IntegerQ[1/(1/EulerPhi[ # ]+1/EulerPhi[ #+1])]&]
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CROSSREFS
| Sequence in context: A192788 A085060 A024546 * A063444 A117061 A089919
Adjacent sequences: A073539 A073540 A073541 * A073543 A073544 A073545
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KEYWORD
| easy,nonn
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AUTHOR
| Benoit Cloitre (benoit7848c(AT)orange.fr), Aug 27 2002
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EXTENSIONS
| Edited by Dean Hickerson (dean.hickerson(AT)yahoo.com), Aug 31 2002
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