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A152218 Numbers n such that sigma_2(n)*sigma_1(n)/sigma_0(n) is a perfect square. 1
1, 4, 529, 2116, 2583, 3249, 3346, 6150, 10332, 12474, 12792, 12996, 28224, 38240, 59245, 85905, 91035, 103607, 142560, 176382, 212949, 236980, 249744, 343620, 360096, 364140, 379050, 414428, 450840, 751530, 787710, 788424, 851796, 1059474, 1132096, 1366407 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Donovan Johnson, Table of n, a(n) for n = 1..200

FORMULA

{n: A001157(n)*A000203(n)/A000005(n) in A000290}.

MATHEMATICA

fQ[n_] := IntegerQ[ Sqrt[ DivisorSigma[2, n] DivisorSigma[1, n]/DivisorSigma[0, n]]]; k = 1; lst = {}; While[k < 1132096, If[ fQ@k, AppendTo[lst, k]; Print@k]; k++ ]; lst (* Robert G. Wilson v, Sep 10 2010 *)

Select[Range[137*10^4], IntegerQ[Sqrt[(DivisorSigma[2, #]DivisorSigma[ 1, #])/ DivisorSigma[ 0, #]]]&] (* Harvey P. Dale, Jun 18 2018 *)

CROSSREFS

Cf. A000005, A001157, A000203, A140480.

Sequence in context: A089668 A257922 A083284 * A152463 A295206 A209608

Adjacent sequences:  A152215 A152216 A152217 * A152219 A152220 A152221

KEYWORD

nonn

AUTHOR

Ctibor O. Zizka, Nov 29 2008

EXTENSIONS

Correct definition recovered by Jack Brennen

12 more terms from R. J. Mathar, Aug 25 2010

More terms from Robert G. Wilson v, Sep 10 2010

STATUS

approved

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Last modified July 17 11:19 EDT 2018. Contains 312701 sequences. (Running on oeis4.)