Won't you have to extract any pairs where one is not a prime - multiples of successive primes. Example (23,25) 25 is not a prime so anything a multiple of 5 has to go, then 7....etc. Or have I got it wrong? The next pair conforming to the pairing is (29,31) then (41,43)

This is where I start wondering how the series can be expressed in mathematical terms....

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