Largest Right-Truncatable Primes allowing 1

Theorem

Let $1$ be temporarily considered to be a prime number.

Under that consideration, the largest right-truncatable prime numbers are:

$1 \, 979 \, 339 \, 333$
$1 \, 979 \, 339 \, 339$


Proof

We have that:

\(\ds \) \(\) \(\ds 1 \, 979 \, 339 \, 333\) is prime
\(\ds \) \(\) \(\ds 1 \, 979 \, 339 \, 339\) is prime


For both, the truncation process is the same:

\(\ds \) \(\) \(\ds 197 \, 933 \, 933\) is the $10 \, 970 \, 817$th prime
\(\ds \) \(\) \(\ds 19 \, 793 \, 393\) is the $1 \, 252 \, 285$th prime
\(\ds \) \(\) \(\ds 1 \, 979 \, 339\) is the $147 \, 488$th prime
\(\ds \) \(\) \(\ds 197 \, 933\) is the $17 \, 815$th prime
\(\ds \) \(\) \(\ds 19 \, 793\) is the $2240$th prime
\(\ds \) \(\) \(\ds 1979\) is the $299$th prime
\(\ds \) \(\) \(\ds 197\) is the $45$th prime
\(\ds \) \(\) \(\ds 19\) is the $8$th prime
\(\ds \) \(\) \(\ds 1\) has been defined temporarily to be prime


This needs considerable tedious hard slog to complete it.
In particular: It remains to be demonstrated that there are no such primes which are larger
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Sources

  • 1986: David Wells: Curious and Interesting Numbers ... (previous) ... (next): $1,979,339,339$
  • 1997: David Wells: Curious and Interesting Numbers (2nd ed.) ... (previous) ... (next): $1,979,339,339$