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Search: id:A091920
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| A091920 |
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Smallest n-digit prime with digits from {1,4,7} only, or 0 if no such prime exists. |
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+0
1
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| 7, 11, 0, 1117, 11117, 0, 1111447, 11111117, 0, 1111111411, 11111111741, 0, 1111111111177, 11111111111411, 0, 1111111111111447, 11111111111111171, 0, 1111111111111111111, 11111111111111111447, 0, 1111111111111111111711
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Any 3k-digit number containing only digits from {1,4,7} has a digit-sum divisible by 3. Therefore the number is divisible by 3 and a(3k) = 0 for all positive integers k.
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FORMULA
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a(k) <= minimum(A036931(k), A036934(k), A036944(k)), a(3k) = 0 and a(A004023(k)) = (10^A004023(k) - 1)/9 = A004022(k) for all positive integers k. (The inequality above holds iff a(k) contains at least one of each digit 1, 4 and 7.).
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CROSSREFS
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Other smallest n-digit primes: A036931 (digits from {1, 4} only), A036934 (digits from {1, 7} only), A036944 (digits from {4, 7} only), A004022 (repunit primes), A004023.
Sequence in context: A123805 A124200 A133346 this_sequence A036934 A070421 A050081
Adjacent sequences: A091917 A091918 A091919 this_sequence A091921 A091922 A091923
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KEYWORD
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base,nonn
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AUTHOR
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Rick L. Shepherd (rshepherd2(AT)hotmail.com), Feb 12 2004
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