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Search: id:A162145
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| A162145 |
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a(n) = the number of non-composites (primes or 1) that are n digits long when written in binary. |
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+0
2
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OFFSET
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1,2
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FORMULA
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a(n)=A036378(n-1), n>2. [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jun 27 2009]
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EXAMPLE
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The consecutive primes 17 (10001 in binary), 19 (10011 in binary), 23 (10111 in binary), 29 (11101 in binary), and 31 (11111 in binary) are the only primes each written with exactly 5 digits in binary. There are 5 of these primes, so a(5) = 5.
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CROSSREFS
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A004676
Sequence in context: A097006 A033306 A136347 this_sequence A145876 A039878 A039886
Adjacent sequences: A162142 A162143 A162144 this_sequence A162146 A162147 A162148
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KEYWORD
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base,more,nonn
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AUTHOR
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Leroy Quet (q1qq2qqq3qqqq(AT)yahoo.com), Jun 25 2009
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