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Search: id:A136131
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| A136131 |
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Values of n such that [sigma(sigma(n))-phi(phi(n))]/n is an integer (the corresponding integral ratios are given in A136132). |
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3
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| 1, 3, 5, 18, 32, 36, 92, 144, 368, 576, 712, 800, 888, 918, 928, 1472, 3193, 4600, 4768, 8800, 9288, 10602, 13032, 16172, 21204, 26856, 36864, 56832, 61792, 84816, 93176, 94208, 96768
(list; graph; listen)
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OFFSET
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1,2
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EXAMPLE
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n=92 is in the sequence because sigma(sigma(92))-phi(phi(92)=sigma(168)-phi(44)=480-20=460=5*92.
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MAPLE
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with(numtheory): a:=proc(n) if type((sigma(sigma(n))-phi(phi(n)))/n, integer) =true then n else end if end proc: seq(a(n), n=1..100000);
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CROSSREFS
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Cf. A136132, A138154, A137600.
Adjacent sequences: A136128 A136129 A136130 this_sequence A136132 A136133 A136134
Sequence in context: A094487 A007516 A039584 this_sequence A143546 A069066 A011964
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KEYWORD
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nonn
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AUTHOR
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Emeric Deutsch (deutsch(AT)duke.poly.edu), Mar 03 2008
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