[seqfan] Re: A046452
israel at math.ubc.ca
israel at math.ubc.ca
Sun Jan 6 03:50:15 CET 2013
Shouldn't it specify that the prime factors are taken in increasing order?
For example, 777= 7*3*37 is not in the sequence. Also perhaps state that
the prime factors need not be distinct.
Robert Israel
University of British Columbia
On Jan 4 2013, Robert G. Wilson v wrote:
>Harvey,
>
> I agree now that you are correct.
>
> Here is the Mmca: fQ[n_] :=
> Block[{t = Table[#[[1]], {#[[2]]}] & /@ FactorInteger[n]}, tt = Flatten@
>IntegerDigits@ t; Length@ Flatten@ t == 3 && tt == Reverse@ tt];
>Select[Range at 30000, fQ]
>
> And it produces: {8, 27, 125, 343, 429, 507, 795, 1309, 1331,
> 1533, 1547, 1587, 2023, 2097, 3633, 3729, 3897, 5289, 5295, 5547, 6597,
> 7833, 8029, 8427, 9583, 9795, 12207, 12795, 13489, 13573, 14133, 14147,
> 14295, 15463, 15549, 15987, 16233, 17295, 20667, 22139, 28273, 28609,
> 28847, 28951, 29729, 29829}
>
>Bob.
>
>-----Original Message-----
>From: SeqFan [mailto:seqfan-bounces at list.seqfan.eu] On Behalf Of Harvey P.
>Dale
>Sent: Friday, January 04, 2013 3:17 PM
>To: Sequence Fanatics Discussion list
>Subject: [seqfan] Re: A046452
>
>Graeme:
> Then would this definition work: "Numbers n with three prime factors
>such that the concatenation of those prime factors is a palindrome"?
> And why are the numbers I mentioned in my earlier email (below) not
>in the current sequence?
> Best,
> Harvey
>
>
>-----Original Message-----
>From: SeqFan [mailto:seqfan-bounces at list.seqfan.eu] On Behalf Of Graeme
>McRae
>Sent: Friday, January 04, 2013 3:04 PM
>To: Sequence Fanatics Discussion list
>Subject: [seqfan] Re: A046452
>
>Because the elements a(n) of sequence A046452 have nothing to do with n.
> It's just a list of numbers, a(n), satisfying the property. I agree with
>you, though, that the word "composite" is superfluous.
>
>--Graeme McRae
>Palmdale, CA
>
>
>On Fri, Jan 4, 2013 at 11:58 AM, Harvey P. Dale <hpd at hpdale.org> wrote:
>
>> I believe I am misunderstanding something about the above
>> sequence. Why aren't these numbers in the sequence: 3729, 28609,
>> 28847, 28951, 29729, 29829? And why does the definition read,
>> "Concatenation of the 3 prime factors of composite a(n) is a
>> palindrome," rather than "Concatenation of the 3 prime factors of n is a
>palindrome"?
>> Clarification would be appreciated.
>> Best,
>> Harvey
>>
>> _______________________________________________
>>
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>>
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