- How rare is it to have 3 prime numbers concatenated left-to-right or right-to-left and still gives you primes?
And if all primes are additive primes (i.e. having prime digit sums) than how rare that would be?
7 with 7=7
29 with 2+9=11
139 with 1+3+9=13
729139 with 7+2+9+1+3+9=31
139297 with 1+3+9+2+9+7=31
Any rough extimate will be do.
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