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A068050 Number of values of k, 1<=k<=n, for which floor(n/k) is prime. 3
0, 1, 1, 1, 2, 2, 3, 2, 2, 4, 5, 3, 4, 5, 6, 5, 6, 5, 6, 6, 7, 9, 10, 6, 7, 9, 9, 9, 10, 10, 11, 9, 10, 12, 14, 11, 12, 13, 14, 13, 14, 13, 14, 14, 15, 17, 18, 13, 14, 16, 17, 18, 19, 17, 19, 18, 19, 21, 22, 18, 19, 20, 21, 19, 21, 22, 23, 23, 24, 26, 27, 21, 22, 23, 24, 24, 26, 27 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,5

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

FORMULA

If p is a prime other than 3, a(p) = a(p-1) + 1. - Franklin T. Adams-Watters, Apr 27 2020

EXAMPLE

a(10) = 4 as floor(10/k) for k = 1 to 10 is 10,5,3,2,2,1,1,1,1,1, respectively; this is prime for k = 2,3,4,5.

MATHEMATICA

a[n_] := Length[Select[Table[Floor[n/i], {i, 1, n}], PrimeQ]]

PROG

(Haskell)

a068050 n = length [k | k <- [1..n], a010051 (n `div` k) == 1]

-- Reinhard Zumkeller, Jan 31 2012

CROSSREFS

Cf. A067514.

Cf. A010051, A205745.

Sequence in context: A069360 A175509 A213023 * A210967 A343534 A275383

Adjacent sequences:  A068047 A068048 A068049 * A068051 A068052 A068053

KEYWORD

easy,nonn

AUTHOR

Amarnath Murthy, Feb 12 2002

EXTENSIONS

Edited by Dean Hickerson, Feb 12 2002

STATUS

approved

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Last modified June 18 04:41 EDT 2021. Contains 345098 sequences. (Running on oeis4.)