@article{10_4064_aa170_2_1,
     author = {Jason P. Bell and Jeffrey C. Lagarias},
     title = {$3x+1$ inverse orbit generating functions
 almost always have natural boundaries},
     journal = {Acta Arithmetica},
     pages = {101--120},
     publisher = {mathdoc},
     volume = {170},
     number = {2},
     year = {2015},
     doi = {10.4064/aa170-2-1},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/aa170-2-1/}
}