The Jacobsthal function 
of a positive integer 
is the least positive
integer 
such that every block of 
consecutive integers contains
an integer relatively
prime to 
.
For example, 
because four consecutive integers always include one
relatively prime to 6, while 2, 3, and 4 form
a block of three that does not.
Jacobsthal Function
See also
Prime Nu Function, Relatively PrimeExplore with Wolfram|Alpha
References
Costello, F. and Watts, P. "An Upper Bound on Jacobsthal's Function." Math. Comput. 84, 1389-1399, 2015. https://doi.org/10.1090/S0025-5718-2014-02896-2.Cite this as:
Weisstein, Eric W. "Jacobsthal Function." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/JacobsthalFunction.html