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Search: id:A117991
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| A117991 |
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Number of distinct rational numbers that can be written as fractions of the first n composite numbers. |
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+0
2
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| 1, 3, 7, 11, 19, 23, 35, 41, 53, 59, 67, 77, 101, 109, 131, 161, 179, 197, 205, 227, 247, 289, 317, 333, 381, 407, 431, 445, 473, 495, 555, 575, 629, 657, 693, 729, 751, 801, 835, 877, 957, 975, 1059, 1097, 1147, 1209, 1235, 1283, 1335, 1367, 1397, 1499, 1539
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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a(n) = 2*A117992(n) + 1.
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EXAMPLE
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n=3, the first 3 composite numbers are 4,6 and 8:
a(3) = #{4/4, 4/6, 4/8, 6/4, 6/6, 6/8, 8/4, 8/6, 8/8} =
= #{1/2, 2/3, 3/4, 1/1, 4/3, 3/2, 2/1} = 7.
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CROSSREFS
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Cf. A018805.
Sequence in context: A160216 A002145 A092109 this_sequence A118260 A018805 A135932
Adjacent sequences: A117988 A117989 A117990 this_sequence A117992 A117993 A117994
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KEYWORD
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nonn
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AUTHOR
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Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Apr 08 2006
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