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Search: id:A068414
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A068414 Numbers n such that sigma(n)=3*n-2*phi(n). +0
5
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)
OFFSET

1,2

COMMENT

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

PROGRAM

(PARI): for(n=1, 500000, if(sigma(n)==3*n-2*eulerphi(n), print1(n, ", ")))

CROSSREFS

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

KEYWORD

easy,nonn

AUTHOR

Benoit Cloitre (benoit7848c(AT)orange.fr), Mar 03 2002

EXTENSIONS

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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Last modified December 11 12:57 EST 2009. Contains 170656 sequences.


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