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A077154
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Smallest k such that there are as many composite numbers less than n as there are between n and k.
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5
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2, 3, 4, 5, 7, 9, 10, 11, 15, 17, 19, 21, 22, 23, 26, 28, 29, 31, 33, 34, 36, 39, 40, 41, 45, 47, 50, 52, 53, 55, 56, 57, 59, 63, 65, 67, 69, 70, 73, 76, 77, 78, 79, 81, 83, 86, 87, 88, 91, 93, 95, 97, 99, 100, 103, 106, 109, 112, 113, 115, 116, 117, 119, 121, 123, 125, 126
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| For n>3, the sequence lists 1 plus every composite number A002808(m), except for those A002808(2m) where A002808(m)+1 is also composite. E.g. 13 = 12+1 is not present because 12 is A002808(6) and A002808(3)+1 = 8+1 = 9 is composite. - Franklin T. Adams-Watters (FrankTAW(AT)Netscape.net), Oct 11 2006
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LINKS
| Diana Mecum, Table of n, a(n) for n = 1..1000
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EXAMPLE
| a(1)=2 because between 1 and 2 there is the same number of composites (none) as below 1. - R. J. Mathar, Sep 08 2008
For n = 12, there are 5 composites less than 12 (4,6,8,9,10), the next 5 composites are 14,15,16,18,20, so a(12) = 21.
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CROSSREFS
| Cf. A077152, A077153, A002808, A092996, A092997, A092998.
Sequence in context: A004050 A123538 A092999 * A077273 A032955 A060526
Adjacent sequences: A077151 A077152 A077153 * A077155 A077156 A077157
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KEYWORD
| nonn
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AUTHOR
| Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Oct 31 2002
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EXTENSIONS
| More terms from Franklin T. Adams-Watters (FrankTAW(AT)Netscape.net), Oct 11 2006
Edited by N. J. A. Sloane (njas(AT)research.att.com), Sep 18 2008 at the suggestion of R. J. Mathar.
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