@article{MS2_1962__10_165799,
     author = {P. Erd\"os},
     title = {On the {Integers} {Relatively} {Prime} to n and a {Number-Theoretic} {Function} {Considered} by {Jacobsthal.}},
     journal = {Mathematica Scandinavica},
     pages = {163--170},
     publisher = {mathdoc},
     volume = {10},
     year = {1962},
     zbl = {0202.33002},
     url = {http://geodesic.mathdoc.fr/item/MS2_1962__10_165799/}
}