Geodesic
On the number of subsets relatively prime to an integer
Journal of integer sequences, Tome 11 (2008) no. 5
Fix a positive integer and a finite set whose elements are in arithmetic progression. We give a formula for the number of nonempty subsets of this set that are coprime to the given integer. A similar formula is given when we restrict our attention to the subsets having the same fixed cardinality. These formulas generalize previous results of El Bachraoui.
Classification : 05A15
Keywords: relatively prime subset, Euler phi function 
@article{JIS_2008__11_5_a7,
     author = {Ayad,  Mohamed and Kihel,  Omar},
     title = {On the number of subsets relatively prime to an integer},
     journal = {Journal of integer sequences},
     year = {2008},
     volume = {11},
     number = {5},
     zbl = {1165.05303},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/JIS_2008__11_5_a7/}
}
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Ayad,  Mohamed; Kihel,  Omar. On the number of subsets relatively prime to an integer. Journal of integer sequences, Tome 11 (2008) no. 5. http://geodesic.mathdoc.fr/item/JIS_2008__11_5_a7/