Unsolved Problems in Number Theory (Texts in Applied Mathematics

Unsolved Problems in Number Theory (Problem Books in Mathematics)

Old and New Unsolved Problems in Plane Geometry and Number Theory (Dolciani Math

100+1 Problems in Advanced Calculus: Problem Books in Mathematics by Paolo Toni

Problems in Group Theory (Dover Books on Mathematics) by Dixon

Problem Books in Mathematics Ser.: Demography Through Problems by John A....

Introduction to Graph Theory (Dover Books on Mathematics) by Trudeau, Richard J.