A107609 a(n) = round(n / pi(n)) = round(n / A000720(n)) where round(x) rounds half to even.

2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 2, 3, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 3, 4, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 3, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4

Offset

2,1

Comments

This sequence grows very slowly. The first n for which a(n) = 5 is 190, then 556 for 6, 1821 for 7, etc. - Alonso del Arte, Feb 27 2012

Links

Zhuorui He, Table of n, a(n) for n = 2..10000

Example

a(6) = 2 because pi(6) = 3 and 6/3 = 2.
a(7) = 2 because pi(7) = 4 and 7/4 = 1.75, which rounds up to 2.

Mathematica

Table[ Round[ n / PrimePi[ n]], {n, 2, 106}]

Prog

(PARI) A107609(n)={my(x = n/primepi(n)); if(denominator((2*x-1)/4)==1, floor(x), round(x)) } \\ Zhuorui He, Sep 12 2025

Crossrefs

Cf. A000720, A107610, A107614, A272231.

Sequence in context: A111859 A156822 A130635 * A243113 A258198 A204562

Adjacent sequences: A107606 A107607 A107608 * A107610 A107611 A107612

Keyword

nonn

Author

Jonathan Vos Post and Robert G. Wilson v, May 17 2005

Status

approved