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A111333
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Number of odd numbers <= n-th prime.
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13
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1, 2, 3, 4, 6, 7, 9, 10, 12, 15, 16, 19, 21, 22, 24, 27, 30, 31, 34, 36, 37, 40, 42, 45, 49, 51, 52, 54, 55, 57, 64, 66, 69, 70, 75, 76, 79, 82, 84, 87, 90, 91, 96, 97, 99, 100, 106, 112, 114, 115, 117, 120, 121, 126, 129, 132, 135, 136, 139, 141, 142, 147, 154, 156, 157
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OFFSET
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1,2
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COMMENTS
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This is A006254 (numbers n such that 2n-1 is prime) with a leading 1. - Lambert Klasen (lambert.klasen(AT)gmx.net), Nov 06 2005
Same as smallest k such that prime(n) divides C(2k,k). - Jonathan Sondow, Jan 20 2016
Positions of records in A046112. - Hugo Pfoertner, Jul 11 2019
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LINKS
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Ray Chandler, Table of n, a(n) for n = 1..10000
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FORMULA
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a(n) = ceiling((prime_n)/2). - Robert G. Wilson v, Nov 07 2005
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MAPLE
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seq(ceil(ithprime(i)/2), i=1..100); # Robert Israel, Jan 20 2016
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MATHEMATICA
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Table[ Ceiling[ Prime[n]/2], {n, 65}] (* Robert G. Wilson v *)
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PROG
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(PARI) a(n)=(prime(n)+1)\2 \\ Charles R Greathouse IV, Sep 16 2015
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CROSSREFS
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Cf. A006254, A046112, A049990, A062875.
Sequence in context: A205805 A246372 A006254 * A047701 A164528 A127963
Adjacent sequences: A111330 A111331 A111332 * A111334 A111335 A111336
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KEYWORD
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nonn,easy
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AUTHOR
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Giovanni Teofilatto, Nov 05 2005
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EXTENSIONS
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More terms from Robert G. Wilson v, Nov 07 2005
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STATUS
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approved
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