% python3
Python 3.8.10 (default, Jun 22 2022, 20:18:18)
[GCC 9.4.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import math
>>> math.gcd(9999999999, 87654321)
9
>>>

Obviously, prime numbers have no factors:

% factor
409993
409993: 409993

Hence, any number smaller than a prime will be coprime with it, because they don't share common factors.
(But larger number can share.)
GCD=1 for coprime numbers.

% bc
bc 1.07.1
Copyright 1991-1994, 1997, 1998, 2000, 2004, 2006, 2008, 2012-2017 Free Software Foundation, Inc.
This is free software with ABSOLUTELY NO WARRANTY.
For details type `warranty'.
scale=5
999999999/87654321
11.40845
3*3*37*333667
111111111
1997*4877
9739369
111111111/9739369
11.40845
(3*3*37*333667)/(1997*4877)
11.40845

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