A081857 Jacobsthal sequence (A001045) as represented in base 4.

0, 1, 1, 3, 11, 23, 111, 223, 1111, 2223, 11111, 22223, 111111, 222223, 1111111, 2222223, 11111111, 22222223, 111111111, 222222223, 1111111111, 2222222223, 11111111111, 22222222223, 111111111111, 222222222223, 1111111111111

Offset: 0

Author

Matthew Vandermast, Apr 11 2003

Keywords

• base
• easy
• nonn

Examples

			a(8)= 1111 because A001045(8)= 85 (in base 10) = 64 + 16 + 4 + 1 = 1 * (4^3) + 1 * (4^2) + 1 * (4^1) + 1.
		

Links

• Eric Weisstein's World of Mathematics, Repunit.

Crossrefs

Cf. A002450.

Programs

Python

from gmpy2 import digits
def A081857(n): return int(digits(((1<Chai Wah Wu, Apr 18 2025

Formula

For n > 0, a(2n) is represented as a string of n 1's and a(2n+1) as a string of (n-1) 2's followed by a 3.