@article{JIS_2010__13_8_a2,
     author = {Lewko,  Mark},
     title = {An improved upper bound for the sum-free subset constant},
     journal = {Journal of integer sequences},
     year = {2010},
     volume = {13},
     number = {8},
     zbl = {1216.11029},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/JIS_2010__13_8_a2/}
}