Truncatable Primes Revisited

The following information is true:

The largest left-truncatable prime in base 10 is the 24-digit number:$$357,686,312,646,216,567,629,137$$A left-truncatable prime is a prime number that contains no zeros and remains prime every time you successively strip away its leading (leftmost) digit. 

However, the same information presented visually where it has a lot more impact.

The largest right truncatable number (73939133) is far shorter because there is the constraint that the right-most digit can only be 1, 3, 7 or 9. A similar inverted pyramid will look like this. Note that 7 is the final prime left as was the case with the right truncatable record holder.

73939133

7393913

739391

73939

7393

739

73

7

If we start with the digit 3, the only other possible choice, and build the longest possible chain of left truncatable primes we end up with the following 20 primes (compared to 24 when we started with the digit 7 - permalink):

3

83

883

6883

76883

676883

6676883

36676883

536676883

3536676883

13536676883

213536676883

7213536676883

57213536676883

957213536676883

4957213536676883

84957213536676883

484957213536676883

6484957213536676883

36484957213536676883

Creating a chain of right-truncatable primes gives us eight primes just as it did when starting with the digit 7 (permalink):

3

37

373

3733

37337

373379

3733799

37337999

We could also start with 2 and in that case we get the following right-truncatable primes:

2

29

293

2939

29399

293999

2939999

29399999