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A066412
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Number of elements in the set phi_inverse(phi(n)).
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0
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2, 2, 3, 3, 4, 3, 4, 4, 4, 4, 2, 4, 6, 4, 5, 5, 6, 4, 4, 5, 6, 2, 2, 5, 5, 6, 4, 6, 2, 5, 2, 6, 5, 6, 10, 6, 8, 4, 10, 6, 9, 6, 4, 5, 10, 2, 2, 6, 4, 5, 7, 10, 2, 4, 9, 10, 8, 2, 2, 6, 9, 2, 8, 7, 11, 5, 2, 7, 3, 10, 2, 10, 17, 8, 9, 8, 9, 10, 2, 7, 2, 9, 2, 10, 8, 4, 3, 9, 6, 10, 17, 3, 9, 2, 17, 7
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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FORMULA
| a(n)=Card( k>0 : cototient(k)=cototient(n) ) where cototient(x)=x-phi(x) - Benoit Cloitre (benoit7848c(AT)orange.fr), May 09 2002
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EXAMPLE
| invphi(6) = [7, 9, 14, 18], thus a(7) = a(9) = a(14) = a(18) = 4.
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MAPLE
| nops(invphi(phi(n)));
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PROG
| (PARI) for(n=1, 150, print1(sum(i=1, 10*n, if(n-eulerphi(n)-i+eulerphi(i), 0, 1)), ", "))
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CROSSREFS
| Sequence in context: A105096 A157790 A070241 * A196048 A176075 A117119
Adjacent sequences: A066409 A066410 A066411 * A066413 A066414 A066415
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KEYWORD
| nonn
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AUTHOR
| Vladeta Jovovic (vladeta(AT)eunet.rs), Dec 25 2001
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