[seqfan] Re: unable to reproduce A152218 (sigma divisibility)
jfb at brennen.net
Wed Aug 25 00:53:30 CEST 2010
Looking again, I'm sure this is what was intended:
sigma_2(n)*sigma(n)/tau(n) is a square.
This also agrees with the terms shown.
Jack Brennen wrote:
> A152218 seems to be those numbers for which:
> sigma_2(n)/sigma(n)/tau(n) is a square of a rational.
> At least that definition agrees out through those first 8 terms.
> That of course is a fairly different description that what is
> actually shown there. :)
> Richard Mathar wrote:
>> I can reproduce A152215, but the very similar A152218 seems to be
>> missing almost all terms:
>> Numbers such that sigma_2(n) * sigma(n) /tau(n) = integer
>> 1, 4, 529, 2116, 2583, 3249, 3346, 6150
>> What is a definition that matches the sequence?
>> The formula says the same as the definition, so it is no aid.
>> The values sigma_2(n) * sigma(n) /tau(n) are
>> 1, 15/2, 20, 49, 78, 150, 200, 1275/4, 1183/3, 585, 732, 980, 1190,
>> 1500, 1560, 10571/5
>> and most of these are integers
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