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A121556 Numbers such that sigma(n)^2 is divisible by UnitarySigma(n)*UnitaryPhi(n). 4
1, 2, 3, 6, 14, 15, 30, 35, 42, 70, 78, 105, 190, 210, 348, 357, 418, 570, 714, 910, 1045, 1144, 1254, 2090, 2296, 2730, 3135, 3432, 4060, 4522, 4674, 5278, 6270, 6888, 10168, 10659, 10824, 12180, 12441, 13566, 14630, 15834, 16770, 17160 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Donovan Johnson, Table of n, a(n) for n = 1..1000

MAPLE

for n from 1 to 20000 do if numtheory[sigma](n)^2 mod (A047994(n)*A034448(n)) = 0 then printf("%d, ", n) ; end if; end do:

MATHEMATICA

f[p_, e_] := (p^(e+1)-1)^2/(p-1)^2/(p^(2*e)-1); seqQ[1] = True; seqQ[n_] := IntegerQ [Times @@ (f @@@ FactorInteger[n])]; Select[Range[17160], seqQ] (* Amiram Eldar, Dec 11 2019 *)

CROSSREFS

Cf. A000203, A121647, A078557, A020492, A034448, A047994.

Sequence in context: A335288 A122839 A258077 * A123041 A078557 A005537

Adjacent sequences:  A121553 A121554 A121555 * A121557 A121558 A121559

KEYWORD

nonn

AUTHOR

Yasutoshi Kohmoto, Sep 12 2006

STATUS

approved

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Last modified October 17 21:17 EDT 2021. Contains 348065 sequences. (Running on oeis4.)