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Burnside, W. Theory of Groups of Finite Order. 2nd ed. Cambridge University Press, Cambridge, 1911; Dover, New York, 1953. A classic. Also available at books.google.com.
[2]

Gallian, J. A. and Winters, S. “Modular Arithmetic in the Marketplace,” The American Mathematical Monthly 95 (1988): 548–51.
[3]

Gallian, J. A. Contemporary Abstract Algebra. 7th ed. Brooks/Cole, Belmont, CA, 2009.
[4]

Hall, M. Theory of Groups. 2nd ed. American Mathematical Society, Providence, 1959.
[5]

Kurosh, A. E. The Theory of Groups, vols. I and II. American Mathematical Society, Providence, 1979.
[6]

Rotman, J. J. An Introduction to the Theory of Groups. 4th ed. Springer, New York, 1995.