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A076647
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Numbers n such that phi(n) + phi(n+1) = sigma(n)/2.
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0
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56, 456, 476, 828, 846, 1196, 2060, 2780, 4484, 7530, 9174, 11420, 11475, 11865, 13454, 22154, 34916, 35385, 52185, 67308, 105798, 140895, 168872, 190840, 219852, 241892, 244074, 267225, 303834, 317564, 330484, 335440, 460292, 580970, 658515
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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EXAMPLE
| phi(56) + phi(57) = 24 + 36 = 60 = 1/2 sigma(56), so 56 is a term of the sequence.
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MAPLE
| with(numtheory): p:=proc(n) if phi(n)+phi(n+1)=sigma(n)/2 then n else fi end: seq(p(n), n=1..2500000); (Deutsch)
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MATHEMATICA
| Select[Range[10^5], EulerPhi[ # ] + EulerPhi[ # + 1] == (1/2)DivisorSigma[1, # ] &]
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CROSSREFS
| Sequence in context: A075283 A205313 A008447 * A187159 A067234 A204832
Adjacent sequences: A076644 A076645 A076646 * A076648 A076649 A076650
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KEYWORD
| nonn
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AUTHOR
| Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Oct 23 2002
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EXTENSIONS
| More terms from Emeric Deutsch (deutsch(AT)duke.poly.edu), Sep 02 2005
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