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A152218
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Numbers n such that sigma_2(n)*sigma_1(n)/sigma_0(n) is a perfect square.
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0
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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
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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FORMULA
| {n: A001157(n)*A000203(n)/A000005(n) in A000290}.
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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 [From Robert G. Wilson v (rgwv(AT)rgwv.com), Sep 10 2010]
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CROSSREFS
| Cf. A000005, A001157, A000203, A140480
Sequence in context: A003393 A089668 A083284 * A152463 A159367 A012770
Adjacent sequences: A152215 A152216 A152217 * A152219 A152220 A152221
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KEYWORD
| nonn
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AUTHOR
| Ctibor O. Zizka (c.zizka(AT)email.cz), Nov 29 2008
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EXTENSIONS
| Correct definition recovered by Jack Brennen; 12 more terms from R. J. Mathar, Aug 25 2010
More terms from Robert G. Wilson v (rgwv(AT)rgwv.com), Sep 10 2010
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