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A090584
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Smallest number m such that n followed by m threes yields a prime or -1 if no solution exists or has been found for n.
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2
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1, 0, 0, 1, 0, -1, 0, 1, -1, 1, 0, -1, 0, 2, -1, 1, 0, -1, 0, 3, -1, 1, 0, -1, 8, 1, -1, 1, 0, -1, 0, 4, -1, 2, 1, -1, 0, 1, -1, 483, 0, -1, 0, 1, -1, 1, 0, -1, 2, 1, -1, 1, 0, -1, 3, 1, -1, 6, 0, -1, 0, 5, -1, 1, 1, -1, 0, 1, -1, 5, 0, -1, 0, 1, -1, 3, 1, -1, 0, 4, -1, 1, 0, -1, 1, 1, -1, 1, 0, -1, 2, 3, -1, 2, 1, -1, 0, 1, -1, 3, 0, -1, 0, 2, -1, 1, 0, -1, 0, 1
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,14
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COMMENTS
| a(n) = 0 if n is already prime. a(n) = -1 for n = any multiple of 3 other than 3 itself. The first 5 record holders in this sequence are 1, 14, 20, 25, 40 with the values 1, 2, 3, 8, 483 respectively. 410 may be the next record holder as no solution has been found for it yet. 410 was tested out to 1250 threes with no prime formed.
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EXAMPLE
| a(25)=8 because eight 3's must be appended to 25 before a prime is formed (2533333333). a(6) = -1 because no matter how many 3's are appended to 6, the resulting number is always divisible by 3 and can therefore not be prime.
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CROSSREFS
| Cf. A083747 (The Wilde Primes, i.e. same operation using ones), A090464 (using sevens), A090465 (using nines).
Sequence in context: A019269 A204459 A035155 * A171400 A128409 A133699
Adjacent sequences: A090581 A090582 A090583 * A090585 A090586 A090587
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KEYWORD
| base,sign
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AUTHOR
| Chuck Seggelin (barkeep(AT)plastereddragon.com), Dec 02 2003
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