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A076665
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phi(n) + phi(n+3) = phi(n+1) + phi(n+2).
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1
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1, 5, 7, 11, 17, 22, 88, 292, 847, 1337, 1691, 7367, 10385, 15430, 51215, 93401, 132535, 211817, 282725, 358852, 359905, 382955, 486772, 507725, 580262, 664870, 700532, 1691081, 1972691, 2637712, 5154625, 5886265, 6510485, 13841531
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| Each term of the sequence marks the start of four consecutive phi-values for which the sum of the means equals the sum of the extremes.
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LINKS
| M. F. Hasler, Table of n,a(n) for n=1,...,44 [From M. F. Hasler (www.univ-ag.fr/~mhasler), Feb 07 2009]
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EXAMPLE
| phi(7) + phi(10) = 6 + 4 =10; phi(8) + phi(9) = 4 + 6 = 10, so 7 is a term of the sequence.
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MATHEMATICA
| Select[Range[10^5], EulerPhi[ # ] + EulerPhi[ # + 3] == EulerPhi[ # + 1] + EulerPhi[ # + 2] &]
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PROG
| (PARI) t=vector(4, i, i)~; c=[[1, 1, -1, -1], [1, -1, -1, 1]]; for(n=1, 10^9, t[n%4+1]=eulerphi(n); c[n%2+1]*t & next; print1(n-3, ", ")) [From M. F. Hasler (www.univ-ag.fr/~mhasler), Feb 07 2009]
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CROSSREFS
| Sequence in context: A192281 A191065 A072249 * A124598 A096215 A144742
Adjacent sequences: A076662 A076663 A076664 * A076666 A076667 A076668
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KEYWORD
| nonn
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AUTHOR
| Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Oct 25 2002
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EXTENSIONS
| Terms beyond a(16) from M. F. Hasler (www.univ-ag.fr/~mhasler), Feb 07 2009
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