@article{NSJOM_1977_7_Nonea_2,
     author = {Ivi\'c Aleksandar},
     title = {Two inequalities 

 for the sum of divisors functions},
     journal = {Novi Sad Journal of Mathematics},
     pages = {17-22},
     year = {1977},
     volume = {7},
     url = {http://geodesic.mathdoc.fr/item/NSJOM_1977_7_Nonea_2/}
}