

A111333


Number of odd numbers <= nth prime.


11



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

1,2


COMMENTS

This is A006254 (numbers n such that 2n1 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


LINKS

Ray Chandler, Table of n, a(n) for n = 1..10000


FORMULA

a(n) = ceiling((prime_n)/2).  Robert G. Wilson v, Nov 07 2005


MAPLE

seq(ceil(ithprime(i)/2), i=1..100); # Robert Israel, Jan 20 2016


MATHEMATICA

Table[ Ceiling[ Prime[n]/2], {n, 65}] (* Robert G. Wilson v *)


PROG

(PARI) a(n)=(prime(n)+1)\2 \\ Charles R Greathouse IV, Sep 16 2015


CROSSREFS

Cf. A006254.
Sequence in context: A205805 A246372 A006254 * A047701 A164528 A127963
Adjacent sequences: A111330 A111331 A111332 * A111334 A111335 A111336


KEYWORD

nonn,easy


AUTHOR

Giovanni Teofilatto, Nov 05 2005


EXTENSIONS

More terms from Robert G. Wilson v, Nov 07 2005


STATUS

approved



