 TOPICS  # Carefree Couple

Define a carefree couple as a pair of positive integers such that and are relatively prime (i.e., ) and is squarefree. Similarly, define a strongly carefree couple as a pair such that and both and are squarefree, and a weakly carefree couple as a pair such that and at least of one and is squarefree. Let be the number of squarefree pairs, the number of carefree couples, the number of strongly carefree couples, and the number of weakly squarefree couples with , illustrated above.

The numbers of squarefree pairs for , 2, ... are 1, 3, 7, 11, 19, 23, 35, 43, 55, ... (OEIS A018805), which has closed forms   (1)   (2)

where is the totient summatory function, is the floor function, and is the Möbius function.

The numbers of carefree couples for , 2, ... are 1, 3, 7, 9, 16, 20, 31, 35, 39, ... (OEIS A118258); the numbers of strongly carefree couples are 1, 3, 7, 7, 13, 17, 27, 27, ... (OEIS A118259); and the numbers of weakly carefree couples are 1, 3, 7, 11, 19, 23, 35, 43, 51, ... (OEIS A118260).

Then   (3)   (4)   (5)   (6)

where the carefree and strongly carefree constants are given by   (7)   (8)   (9)   (10)   (11)   (12)   (13)   (14)   (15)   (16)   (17)   (18)

(OEIS A065464, A065473, and A118261; Moree 2005), where is the Riemann zeta function.

Prime Products, Squarefree

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## References

Finch, S. R. "Carefree Couples." §2.5.1 in Mathematical Constants. Cambridge, England: Cambridge University Press, pp. 110-112, 2003.Moree, P. "Counting Carefree Couples." 30 Sep 2005. http://arxiv.org/abs/math.NT/0510003.Niklasch, G. "Some Number-Theoretical Constants." http://www.gn-50uma.de/alula/essays/Moree/Moree.en.shtml.Schroeder, M. R. Number Theory in Science and Communication: With Applications in Cryptography, Physics, Digital Information, Computing, and Self-Similarity, 3rd ed. New York: Springer-Verlag, p. 54, 1997.Sloane, N. J. A. Sequences A015614, A018805, A065464, A065473, A118258, A118259, A118260, and A118261 in "The On-Line Encyclopedia of Integer Sequences."

Carefree Couple

## Cite this as:

Weisstein, Eric W. "Carefree Couple." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/CarefreeCouple.html