A059485 Highest prime factor is greater than 3.

5, 7, 10, 11, 13, 14, 15, 17, 19, 20, 21, 22, 23, 25, 26, 28, 29, 30, 31, 33, 34, 35, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 49, 50, 51, 52, 53, 55, 56, 57, 58, 59, 60, 61, 62, 63, 65, 66, 67, 68, 69, 70, 71, 73, 74, 75, 76, 77, 78, 79, 80, 82, 83, 84, 85, 86, 87, 88, 89

Offset: 1

Author

Simone Caramel (simonecaramel(AT)libero.it), Feb 04 2001

Keywords

• nonn
• easy

Comments

Numbers n such that A006530(n) > 3. - Felix Fröhlich, Dec 22 2016

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..9933

Crossrefs

Complement of A003586. Cf. A007310 for numbers whose smallest prime factor (if there is one) is greater than 3.

Cf. A006530.

Programs

Magma

[n: n in [1..100] | not PrimeDivisors(n) subset [2, 3]]; // Vincenzo Librandi, Dec 22 2016

Mathematica

fQ[n_]:=! PowerMod[6, n, n]==0; Select[Range [100], fQ] (* Vincenzo Librandi, Dec 22 2016 *)

PARI

is(n)=n>>=valuation(n,2); n/=3^valuation(n,3); n>1 \\ Charles R Greathouse IV, Jul 06 2016; corrected by Michel Marcus, May 19 2022

Python

from sympy import integer_log
def A059485(n):
    def f(x): return n+sum((x//3**i).bit_length() for i in range(integer_log(x,3)[0]+1))
    m, k = n, f(n)
    while m != k: m, k = k, f(k)
    return m # Chai Wah Wu, Sep 16 2024

Formula

a(n) ~ n. - Charles R Greathouse IV, Jul 06 2016

Extensions

More terms from Henry Bottomley, Feb 05 2001