Charles Babbage, Chapter VIII – Of the Analytical Engine, Larger Numbers Treated, Passages from the Life of a Philosopher, Longman Green, London, 1864; page 125.
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A. A. Karatsuba (1995). "The Complexity of Computations"(PDF). Proceedings of the Steklov Institute of Mathematics. 211: 169–183. Translation from Trudy Mat. Inst. Steklova, 211, 186–202 (1995){{cite journal}}: CS1 maint: postscript (link)