A061785 a(n) = m such that 2^m < 5^n < 2^(m+1).

2, 4, 6, 9, 11, 13, 16, 18, 20, 23, 25, 27, 30, 32, 34, 37, 39, 41, 44, 46, 48, 51, 53, 55, 58, 60, 62, 65, 67, 69, 71, 74, 76, 78, 81, 83, 85, 88, 90, 92, 95, 97, 99, 102, 104, 106, 109, 111, 113, 116, 118, 120, 123, 125, 127, 130, 132, 134, 136, 139, 141, 143, 146, 148

Offset: 1

Author

Lekraj Beedassy, May 09 2003

Keywords

• nonn
• easy

Comments

The Beatty sequence for log_2(5) (A020858). The asymptotic density of this sequence is log_5(2) (A152675). - Amiram Eldar, Apr 09 2021

One less than the length of 5^n written in binary. Could and should be extended to a(0) = 0 (with definition corrected to "2^m <= ..."). - M. F. Hasler, Apr 17 2024

Examples

			a(2) = 4 since 2^4 < 5^2 < 2^(4+1).
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A020858, A152675.

Cf. A118738 (Hamming weight of 5^n).

Programs

Mathematica

Table[Floor[n*Log2[5]], {n, 100}] (* Amiram Eldar, Apr 09 2021 *)

PARI

a(n) = floor(n*log(5)/log(2)) \\ Michel Marcus, Jul 27 2013

Python

def A061785(n): return (5**n).bit_length()-1 # Chai Wah Wu, Jul 22 2025

Formula

a(n) = floor(n*log_2(5)). - M. F. Hasler, Apr 17 2024

Extensions

Corrected and extended by John W. Layman, May 09 2003