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Search: id:A011254
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| A011254 |
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Numbers n such that phi(n) + sigma(n) = 4n. |
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+0
4
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| 23760, 59400, 153720, 4563000, 45326160, 113315400, 402831360, 731601000, 803685120, 865950624, 919501200, 1178491680, 3504597120, 3786686400
(list; graph; listen)
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OFFSET
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1,1
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REFERENCES
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R. K. Guy, Divisors and desires, Amer. Math. Monthly, 104 (1997), 359-360.
Zhang Ming-Zhi (typescript submitted to Unsolved Problems section of Monthly, Oct 01 1996.
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EXAMPLE
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phi(23760)+sigma(23760)=5760+89280=4*23760, so 23760 is in the sequence.
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CROSSREFS
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Cf. A000010, A000203, A011251, A011774, A015704.
Sequence in context: A031847 A069334 A118061 this_sequence A066234 A084691 A084692
Adjacent sequences: A011251 A011252 A011253 this_sequence A011255 A011256 A011257
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KEYWORD
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nonn,nice
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AUTHOR
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njas
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EXTENSIONS
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More terms from Jud McCranie (j.mccranie(AT)comcast.net)
1178491680 from Farideh Firoozbakht, Jan 31 2006
2 more terms from Jud McCranie (j.mccranie(AT)comcast.net), Jan 31 2006
24 divides all known terms of the sequence. If this is true for the next five terms then they are 6429564000, 14924714400, 25310621952, 26998616736 and 53138687040. - Farideh Firoozbakht, Mar 11 2006
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