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 
(Costello and Watts 2015). 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