Method for finding number of odd-length figurate reps of x

[Andrew Plewe]

See:
A007488  Primes whose reversal is a square.

--- JEREMY GARDINER <jeremy.gardiner at btinternet.com>
wrote:

> What number comes next in the sequence: 61, 691,
> 163, 487, 4201, ?
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>   Found at:  http://nces.ed.gov/nceskids/index.asp
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>   Scroll down for the answer ...
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>   Jeremy Gardiner
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>   9631. The sequence consists of the prime numbers
> which, when their digits are reversed, are perfect
> squares. 
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>   <correctness of the answer has not been checked>
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Hello seqfans,

I am trying to build a sequence corresponding to the following property of 2421:

2421 = prime(2)^2 + prime(4)^4 + prime(2)^2 + prime(1)^1.


My Mathematica coding is too slow,  I can only check up to 100000000.

This sequence is obviously finite. I know theoretical ways to speed up my code, but practically I am not that good yet :-)

If there are no other numbers like this, it would be very interesting for me personally, as it would mean that 2421 is the ONLY number with this property. In my number gossip database there are about 1000 unique properties and only a very small proportion correspond to "the only" property (as opposed to "the smallest" property). 

Uniqueness of this property would mean a great deal to me especially as this number is relatively big. If there are other numbers like this, there would be a new sequence. So we win in any case :-)

Best, Tanya


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