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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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1
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1, 2, 2, 2, 5, 7, 13, 23, 43, 75, 137, 255, 464, 872, 1612, 3030, 5709, 10749, 20390, 38635, 73586, 140336, 268216, 513708, 985818, 1894120, 3645744, 7027290, 13561907, 26207278, 50697537, 98182656, 190335585, 369323305, 717267168
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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FORMULA
| a(n)=A036378(n-1), n>2. [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jun 27 2009]
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EXAMPLE
| 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
| A004676
Same as A036378 except for a(1). [From Franklin T. Adams-Watters (FrankTAW(AT)Netscape.net), May 25 2010]
Sequence in context: A136347 A145876 A039878 * A039886 A109523 A008295
Adjacent sequences: A162142 A162143 A162144 * A162146 A162147 A162148
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KEYWORD
| base,nonn
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AUTHOR
| Leroy Quet, Jun 25 2009
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EXTENSIONS
| More terms from Franklin T. Adams-Watters (FrankTAW(AT)Netscape.net), May 25 2010
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