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A078557 Squarefree balanced numbers (i.e., squarefree members of A020492). 4
1, 2, 3, 6, 14, 15, 30, 35, 42, 70, 78, 105, 190, 210, 357, 418, 570, 714, 910, 1045, 1254, 2090, 2730, 3135, 4522, 4674, 5278, 6270, 10659, 12441, 13566, 14630, 15834, 16770, 20026, 21318, 23374, 24871, 24882, 24969, 25070, 25714, 27170, 29029 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Donovan Johnson, Table of n, a(n) for n = 1..10000

EXAMPLE

210 = 2*3*5*7, sigma(210) = 576, phi(210) = 48, 576/48 = 12.

MATHEMATICA

Do[s=DivisorSigma[1, n]/EulerPhi[n]; If[IntegerQ[s]&&!Equal[MoebiusMu[n], 0], k=k+1; Print[n]], {n, 1, 2100000}]

CROSSREFS

Cf. A020492.

Sequence in context: A258077 A121556 A123041 * A005537 A306600 A282351

Adjacent sequences:  A078554 A078555 A078556 * A078558 A078559 A078560

KEYWORD

nonn

AUTHOR

Labos Elemer, Dec 06 2002

STATUS

approved

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Last modified October 27 07:47 EDT 2021. Contains 348272 sequences. (Running on oeis4.)