@article{MS2_1975__37_166429,
     author = {Timo Ojala},
     title = {Sums of roots of unity.},
     journal = {Mathematica Scandinavica},
     pages = {83--101},
     publisher = {mathdoc},
     volume = {37},
     year = {1975},
     zbl = {0339.12005},
     url = {http://geodesic.mathdoc.fr/item/MS2_1975__37_166429/}
}