Talk:Truncatable prime
Latest comment: 3 years ago by PrimeHunter in topic Two-sided primes
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Two-sided primes
editarticle does not address if there are prime truncatable both right and left, or for that matter a proof they eithr do or do not exist. -- Cimon Avaro; on a pogostick. 18:32, 12 January 2007 (UTC)
- I have added "two-sided primes", primes which are both left-truncatable and right-truncatable, to the article. PrimeHunter 15:12, 8 February 2007 (UTC)
- All but four of these are also left-and-right truncatable: 2, 3, 5, 7, 23, 37, 53, 73, 373, 3137, 3797. Would these be "three-sided"? -- DewiMorgan (talk) 15:21, 17 May 2021 (UTC)
- @DewiMorgan: I haven't found any use of that name. They are in OEIS:A284060 with no name. Wikipedia does not invent names. PrimeHunter (talk) 20:53, 17 May 2021 (UTC)
- All but four of these are also left-and-right truncatable: 2, 3, 5, 7, 23, 37, 53, 73, 373, 3137, 3797. Would these be "three-sided"? -- DewiMorgan (talk) 15:21, 17 May 2021 (UTC)
Bound on count
editHow can it be known that there is a bound on the number of truncatable primes? 85.166.78.90 (talk) 20:03, 2 November 2008 (UTC)
- It's easy to make an exhaustive computer search in base 10 by starting with one-digit primes and trying to add digits to the start (left-truncatable) or end (right-truncatable) while keeping it a prime. I and many others have done it. I think my exhaustive search took less than a second on a PC. It gets harder for bases significantly above 10 when there are a lot of possible digits to add. There are left-truncatable base counts in oeis:A076623 and right-truncatable in oeis:A076586. PrimeHunter (talk) 01:06, 3 November 2008 (UTC)
- The rules must be changed to give something computationally challenging in base 10. http://www.primepuzzles.net/puzzles/puzz_131.htm studies a case where the truncation doesn't have to end with a one-digit prime (or equivalently that addition of digits can start from a multidigit prime). There I wrote: "96842946512633189183337876922083307 is the smallest (and only known) prime which can be truncated more times than the largest left-truncatable prime". The truncation ends with 76922083307. The next number 6922083307 is composite. PrimeHunter (talk) 01:20, 3 November 2008 (UTC)