Enumeration of certain finite semigroups of transformations. - Abdullahi Umar (Discret. Math., 1998)

Some Combinatorial Properties of the Symmetric Monoid. - Abdullahi Laradji; Abdullahi Umar (Int. J. Algebra Comput., 2011)

On The Number Of Subpermutations With Fixed Orbit Size. - Abdallah Laradji; Abdullahi Umar (Ars Comb., 2013)

Combinatorial results for certain semigroups of partial isometries of a finite chain. - Fatma Al-Kharousi; R. Kehinde; Abdullahi Umar (Australas. J Comb., 2014)

Combinatorial results for order-preserving partial injective contraction mappings. - Ahmed Bayo Musa; Nadia Aldhamri; Fatma Al-Kharousi; Georg Klein; Abdullahi Umar (Contributions Discret. Math., 2024)

Geostatistical and multivariate analysis of phosphate evolution and its relationship with heavy metals in shallow groundwater in a Semi-Arid Basin. - Saadu Umar Wali; Noraliani Binti Alias; Abdulqadir Abubakar Usman; Abdullahi Umar; Nasiru Muhammad; Ismail Usman Kaoje; Buhari Samaila; Basiru Aliyu; Habiba Muhammad Ladan; Mudassiru Atiku; Sa'ad Ibrahim (Earth Sci. Informatics, 2025)