A158581 Numbers having in binary representation at least two ones and two zeros.

9, 10, 12, 17, 18, 19, 20, 21, 22, 24, 25, 26, 28, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 48, 49, 50, 51, 52, 53, 54, 56, 57, 58, 60, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 96, 97

Offset: 1

Author

Reinhard Zumkeller, Apr 16 2009

Keywords

• nonn
• base

Links

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

Crossrefs

Intersection of A158582 and A057716.

Cf. A007088, A000120, A023416

Programs

Mathematica

Select[Range[100],Min[DigitCount[#,2]]>1&] (* Harvey P. Dale, Mar 09 2013 *)

Python

def ok(n): b = bin(n)[2:]; return b.count('0') >= 2 and b.count('1') >= 2
print(list(filter(ok, range(98)))) # Michael S. Branicky, Sep 10 2021

Python

def A158581(n):
    def f(x):
        c = n+((l:=(x+1).bit_length())*(l+1)>>1)-3
        m = bin(x+1)[2:].find('0')
        c += m if m>-1 else l
        return c
    m, k = n, f(n)
    while m != k: m, k = k, f(k)
    return m # Chai Wah Wu, Dec 24 2024

Formula

A023416(a(n)) > 1; A000120(a(n)) > 1.