[seqfan] Re: tau and sigma

[israel at math.ubc.ca]

tau = number of divisors, sigma = sum of divisors.

Cheers,
Robert

On Aug 31 2015, Allan Wechsler wrote:

>My first guess at the meanings of tau() and sigma() were wrong; perhaps a
>little more context would be good.
>
> On Fri, Jul 31, 2015 at 9:16 AM, Frank Adams-Watters 
> <franktaw at netscape.net> wrote:
>
>> Is the sequence of all numbers n with tau(n+1) = tau(n-1) and 
>> sigma(n-1) = sigma(n+1) in the database? Likewise for the second one? 
>> I'm not sure either of those should be accepted, but don't even consider 
>> adding a sequence "primes with property P" unless "numbers with property 
>> P" is already there, or at the very least is submitted at the same time.
>>
>> (Of course, this doesn't apply if P is really only applicable to primes,
>> e.g. if it involves primitive roots.)
>>
>> Franklin T. Adams-Watters
>>
>> -----Original Message-----
>> From: юрий герасимов <2stepan at rambler.ru>
>> To: seqfan <seqfan at list.seqfan.eu>
>> Sent: Fri, Jul 31, 2015 1:07 am
>> Subject: [seqfan] tau and sigma
>>
>>
>>
>> Dear SeqFans,
>>
>> 919, 13333097, 13358407, 70779463, 105125921, 110495719,
>> 292840063, 321860263, 415520359, 617684959, 628112717, 993590681,...
>>
>> --> primes
>> p satisfyng tau(p + 1) = tau(p - 1) and sigma(p + 1) = sigma(p - 1);
>>
>> 53,
>> 20543, 47843, 32003407, 59808803, 96144127, 113561243, 238818893,
>> 1020720293,
>> ...
>>
>> --> primes p satisfyng tau(p + 2) = tau(p - 2) and sigma(p + 2) = 
>> sigma(p - 2).
>>
>> 1-th sequence or 2-th sequence is of general interest?
>>
>> Thanks.
>> JSG.
>>
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