1. Department of Mathematics and Computers Sciences, University of Agadez, Agadez, Niger
2. Department of Applied Mathematics and Institute Carlos I of Theoretical and Computational Physics, University of Granada, Fuentenueva s/n, 18071 Granada, Spain
3. Department of Mathematics, University of Jaen, Campus Las Lagunillas s/n, 23071 Jaen, Spain
4. Institute Carlos I of Theoretical and Computational Physics, University of Granada, Fuentenueva s/n, 18071 Granada, Spain