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Search: id:A068414
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| A068414 |
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Numbers n such that sigma(n)=3*n-2*phi(n). |
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+0
5
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| 1, 12, 56, 260, 992, 1976, 2156, 2754, 16256, 25232, 41072, 133984, 145888, 1100864, 1270208, 1439552, 2237888, 4729664, 67100672, 75398912, 171627376, 277060144, 473089984
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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Complete up to 50000000. - Rick L. Shepherd (rshepherd2(AT)hotmail.com), Mar 28 2002
If 2^p-1 is prime(a Mersenne prime) and n=2^p*(2^p-1) then n is in the sequence because 3*n-2*phi(n)=3*2^p*(2^p-1)-2^p*(2^p-2) =2^p*(2^(p+1)-1)=sigma(2^p-1)*sigma(2^p)=sigma(2^p*(2^p-1))= sigma(n). - Farideh Firoozbakht (mymontain(AT)yahoo.com), Dec 31 2005
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PROGRAM
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(PARI): for(n=1, 500000, if(sigma(n)==3*n-2*eulerphi(n), print1(n, ", ")))
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CROSSREFS
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Cf. A068418, A069719, A069737.
Sequence in context: A035289 A009827 A068418 this_sequence A081756 A027147 A095724
Adjacent sequences: A068411 A068412 A068413 this_sequence A068415 A068416 A068417
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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 03 2002
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EXTENSIONS
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More terms from Rick L. Shepherd (rshepherd2(AT)hotmail.com), Mar 28 2002
More terms from Labos E. (labos(AT)ana.sote.hu), Apr 03 2002
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