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A084820
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Numbers n such that n, sigma(n) and phi(n) form an integer triangle, where sigma=A000203 is the divisor sum and phi=A000010 the totient.
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2
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1, 3, 5, 7, 9, 11, 13, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43, 47, 49, 51, 53, 55, 57, 59, 61, 65, 67, 69, 71, 73, 77, 79, 81, 83, 85, 87, 89, 91, 93, 95, 97, 99, 101, 103, 107, 109, 111, 113, 115, 117, 119, 121, 123, 125, 127, 129, 131, 133, 137
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OFFSET
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1,2
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COMMENTS
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a(n)<=A000203(a(n))+A000010(a(n)), A000203(a(n))<=a(n)+A000010(a(n)), A000010(a(n))<=a(n)+A000203(a(n)); values are odd, see A084821 for odd numbers which are not in the sequence.
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LINKS
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Table of n, a(n) for n=1..63.
Eric Weisstein's World of Mathematics, Divisor Function
Eric Weisstein's World of Mathematics, Totient Function
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EXAMPLE
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n=5, a(5)=9: phi(9)=6, sigma(9)=13: (6,9,13)=(A070080(176), A070081(176), A070082(176)).
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PROG
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(PARI) is(n)=eulerphi(n)+n>sigma(n) \\ Charles R Greathouse IV, Feb 19 2013
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CROSSREFS
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Cf. A046022.
Sequence in context: A184591 A033040 A200982 * A151991 A165468 A112372
Adjacent sequences: A084817 A084818 A084819 * A084821 A084822 A084823
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KEYWORD
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nonn
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AUTHOR
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Reinhard Zumkeller, Jun 04 2003
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STATUS
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approved
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