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Search: id:A068420
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| A068420 |
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Numbers n such that sigma(n)=4*(n-phi(n)). |
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+0
2
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| 3, 99, 168, 780, 1836, 2976, 5928, 6201, 6468, 13888, 48768, 75696, 123216, 227584, 285948, 401952, 437664, 1003000, 2058732, 3302592, 3810624, 4031488, 4258496, 4318656, 6713664, 14188992, 32021613, 93298284
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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If 2^p-1 is a prime (a Mersenne prime) greater than 3 then 3*2^p*(2^p-1) is in the sequence (the proof is easy). The sequence A110075 gives such terms of this sequence. - Farideh Firoozbakht (f.firoozbakht(AT)math.ui.ac.ir), Jul 27 2005
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PROGRAM
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(PARI) for(n=1, 100000000, if(sigma(n)==4*(n-eulerphi(n)), print1(n, ", ")))
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CROSSREFS
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Cf. A000668, A110075.
Adjacent sequences: A068417 A068418 A068419 this_sequence A068421 A068422 A068423
Sequence in context: A107173 A100494 A057014 this_sequence A128296 A037114 A069457
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KEYWORD
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easy,nonn
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AUTHOR
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Benoit Cloitre (benoit7848c(AT)orange.fr), Mar 02 2002
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EXTENSIONS
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More terms from Rick L. Shepherd (rshepherd2(AT)hotmail.com), Apr 03 2002
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