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A068414
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Numbers n such that sigma(n) = 3n - 2*phi(n).
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4
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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, 538178048, 558585344, 629225984, 1192258048, 1863840112, 2181070592, 4534854656
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| 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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PROG
| (PARI) for(n=1, 500000, if(sigma(n)==3*n-2*eulerphi(n), print1(n, ", ")))
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CROSSREFS
| Cf. A068418, A069719, A069737.
Sequence in context: A035289 A009827 A068418 * A199316 A081756 A027147
Adjacent sequences: A068411 A068412 A068413 * A068415 A068416 A068417
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KEYWORD
| nonn,changed
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AUTHOR
| Benoit Cloitre (benoit7848c(AT)orange.fr), Mar 03 2002
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EXTENSIONS
| More terms (complete up to 50000000). - Rick L. Shepherd (rshepherd2(AT)hotmail.com), Mar 28 2002
More terms from Labos E. (labos(AT)ana.sote.hu), Apr 03 2002
a(24)-a(30) from Donovan Johnson (donovan.johnson(AT)yahoo.com), Feb 08 2012
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