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Search: id:A097646
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| A097646 |
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Numbers n such that n=phi(phi(n)+sigma(n)). |
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+0
4
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| 1, 2, 6, 10, 20, 22, 46, 48, 58, 82, 106, 166, 178, 180, 208, 226, 262, 346, 358, 382, 466, 478, 502, 562, 586, 718, 838, 862, 864, 886, 982, 1018, 1120, 1186, 1282, 1306, 1318, 1366, 1368, 1438, 1486, 1522, 1618, 1822, 1906, 2026, 2038, 2062, 2098, 2206
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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If n=2*p where p is a Sophie Germain odd prime then n is in the sequence, the proof is obvious.
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LINKS
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C. K. Caldwell, The Prime Glossary, Sophie Germain prime.
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EXAMPLE
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22 is in the sequence because phi(22)=10, sigma(22)=36 & phi(10+36)=22.
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MATHEMATICA
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Do[If[n==EulerPhi[EulerPhi[n]+DivisorSigma[1, n]], Print[n]], {n, 2400}]
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CROSSREFS
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Cf. A097652, A005384, A097645, A018784.
Adjacent sequences: A097643 A097644 A097645 this_sequence A097647 A097648 A097649
Sequence in context: A028247 A065054 A128165 this_sequence A077084 A007926 A096338
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KEYWORD
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nonn
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AUTHOR
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Farideh Firoozbakht (f.firoozbakht(AT)math.ui.ac.ir), Sep 08 2004
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