A superprime is an integer such that all its left-to-right initial segments are prime (e.g. 7331 whose segments are 7, 73, 733, and 7331, all prime).
There is a largest superprime.
Find it.
Source: USA Computing Olympiad,
Feb 1995.
1. Lemma (Confucius): "If language is not correct, then what is said is not what is meant; if what is said is not what is meant, then what must be done remains undone....the people will stand about in helpless confusion. Hence there must be no arbitrariness in what is said. This matters above everything."
2. Rectification procedure: {'superprime'} = right-truncatable prime.
3. See Sloane A024770 Right-truncatable primes: every prefix is prime: (83) 73939133.
Total time taken: 1.2 minutes (it took longer to do the post)
Edited on October 20, 2010, 12:38 pm
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Posted by broll
on 2010-10-20 12:34:48 |
Another method.
