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A121287 Numbers such that Sigma(n)*UnitarySigma(n) is divisible by UnitaryPhi(n)*n. 1
1, 6, 60, 140, 8190, 32760 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

No more terms up to 10^8. - Michel Marcus, Jan 24 2019

a(7) > 10^12, if it exists. - Giovanni Resta, Jun 07 2019

LINKS

Table of n, a(n) for n=1..6.

FORMULA

{n: (n*A047994(n)) | (sigma(n)*A034448(n)) }.

PROG

(PARI) uphi(n) = my(f=factor(n)~); prod(i=1, #f, f[1, i]^f[2, i]-1); \\ A047994

usigma(n) = sumdivmult(n, d, if(gcd(d, n/d)==1, d)); \\ A034448

isok(n) = ((sigma(n)*usigma(n)) % (n*uphi(n))) == 0; \\ Michel Marcus, Jan 24 2019

CROSSREFS

Cf. A000203, A034448, A047994, A121288.

Sequence in context: A337691 A126576 A232181 * A069072 A256442 A296317

Adjacent sequences:  A121284 A121285 A121286 * A121288 A121289 A121290

KEYWORD

nonn,more

AUTHOR

Yasutoshi Kohmoto, Sep 05 2006

STATUS

approved

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Last modified May 13 19:36 EDT 2021. Contains 343868 sequences. (Running on oeis4.)