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Search: id:A090178
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| A090178 |
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a(1) = 2; for n > 1, a(n) = n+prime(n-1). |
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6
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| 2, 4, 6, 9, 12, 17, 20, 25, 28, 33, 40, 43, 50, 55, 58, 63, 70, 77, 80, 87, 92, 95, 102, 107, 114, 123, 128, 131, 136, 139, 144, 159, 164, 171, 174, 185, 188, 195, 202, 207, 214, 221, 224, 235, 238, 243, 246, 259, 272, 277, 280, 285, 292, 295, 306, 313, 320, 327
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Sum of index n and the corresponding n-th term of non-composite numbers (A008578).
Does n > 2 exist such that n*prime(n-1)/(n+prime(n-1)), i.e. A164931(n)/a(n) is an integer? [From Jaroslav Krizek (jaroslav.krizek(AT)atlas.cz), Aug 31 2009]
Complement of A171508(n). [From Jaroslav Krizek (jaroslav.krizek(AT)atlas.cz), Dec 13 2009]
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REFERENCES
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M. Feenstra, P. J. Carter and C. P. Harding, The Ultimate I.Q. Book, Wardlock, see p. 99.
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FORMULA
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a(n) = n+A008578(n). - David Wasserman (dwasserm(AT)earthlink.net), May 20 2008
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EXAMPLE
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a(2) = 2+prime(1) = 4; a(5) = 5+prime(4) = 12; a(9) = 9+prime(8) = 28.
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PROGRAM
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(MAGMA) [ n eq 1 select 2 else n+NthPrime(n-1): n in [1..58] ]; [From Klaus Brockhaus, Sep 09 2009]
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CROSSREFS
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The published version (A048171) is said to be incorrect.
Sequence in context: A022778 A156022 A048171 this_sequence A080548 A080556 A064985
Adjacent sequences: A090175 A090176 A090177 this_sequence A090179 A090180 A090181
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KEYWORD
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nonn
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AUTHOR
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Pab Ter (pabrlos(AT)yahoo.com), May 29 2004
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EXTENSIONS
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Definition corrected, second comment and example edited by Klaus Brockhaus (klaus-brockhaus(AT)t-online.de), Sep 09 2009
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