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Search: id:A138154
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| A138154 |
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Numbers n such that sigma(sigma(n))-phi(phi(n))=2n. |
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3
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OFFSET
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1,1
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COMMENT
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No other term <10^6.
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EXAMPLE
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3193 is in the sequence because sigma(sigma(3193))-phi(phi93193))=sigma(3328)-phi(3060)=7154-768=6386=2*3193.
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MAPLE
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with(numtheory): a:=proc(n) if sigma(sigma(n))-phi(phi(n))=2*n then n else end if end proc: seq(a(n), n=1..1000000);
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CROSSREFS
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Cf. A136131, A136132, A137600.
Sequence in context: A062655 A090807 A167483 this_sequence A126334 A068635 A156695
Adjacent sequences: A138151 A138152 A138153 this_sequence A138155 A138156 A138157
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KEYWORD
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more,nonn,bref
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AUTHOR
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Emeric Deutsch (deutsch(AT)duke.poly.edu), Mar 03 2008
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